Flatbed and composite panel build on Dodge 2500


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So a few years ago, I built a nice Ford F-650 to comfortably haul 4 people and sleep up to 6 for our families travels, we race cross country and hare scrambles plus do a lot of off road riding. In the past we used your typical RV but after killing 2 motorhomes, 2 travel trailers, and having the family space requirements exceed the limitations of our Bigfoot camper on our F-450 (the ONLY camper that had no issues after 2 years of good use) the F-650 was born. We are running it for the 4th consecutive year, with no issues, 50% of our travel is on rough unimproved gravel roads. It is light for its size, roomy, safe, warm, lots of water and power, we are able to run extended periods without issue, it has travelled through 2 provinces and 6 states in the name of fun.

Recently my son and I have been starting to do a lot more day trips, which is usually 300-500 km's of driving plus a full day of hard riding, it would be nice to shoot out the night before, and be there for the crack of dawn, but I don't like driving the big rig out with the trailer for one nights sleep for just the 2 of us. It is always stocked and ready to go for the whole family which is usually a minimum of 3 days supplies, plus she burns diesel at 9 MPG so in this circumstance it's a little bit of a job to use it. My F-650 has proven itself, and I have got a lot of positive feedback from the racing community, a lot of people deal with the same issues we used to. So after a lot of inquiries I decided to investigate the possibilities of building a platform that would service our sport as well as survive the kind of travelling we do, like a lot of people on this forum do.

The build is a 2004 Dodge 2500 crew cab long box diesel, it's my truck, with only 150 000 KM's on the odometer, and in mint well maintained condition. It's been a great truck and if I replace it, I want to be able to unbolt everything and drop it on to a new chassis. The deck will be aluminum, the build will be extremely focused on the limitations within the factory chassis and vehicle capacities, keep unnecessary weight out, and keep function number 1 and aesthetics right behind. The camper will follow the same philosophies, I have been working with composite panels for a few years in some very harsh environments, and I have designed a line of extrusions that will make the build relatively straight forward, and extremely strong with a little bit of flexibility built into the entire structure.


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First step

Weigh it! What can it haul?

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Front and rear axle weights stock with box and a Trail Ready rear bumper. 2110 KG front (4650 lb) and 1260 KG rear (2777 lb), total 3370 KG (7427 lb). Heavy truck! That is with a Trail Ready front bumper, 4" Fabtech lift, and 35" Generals on aluminum wheels.


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How flexible is it?

I considered a 3 point mounting system, everybody need that right? Well why don't we find out what we are dealing with. It's not like the old days when the box of the old Chevy would beat the required clearance into the cab in the rough stuff, truck chassis suspension has evolved a bit. I took a forklift and lifted the right rear tire until the left rear tire just left the ground, with a couple straight edges across the box I snapped a few different pics to illustrate the amount of frame flex we are dealing with, not much, 5/8 - 11/16" from what I could physically measure. You can see the top of the rear tire is pretty close to flush with the top of the frame, you can see daylight on the other side, the trite was 22" off the ground before any other tire lifted, the front suspension reaction was equally balanced.



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After establishing a few basic parameters, I stripped off the box and rear bumper, I want to find out what they weigh and the effect on axle weights, all weights were with a half tank of fuel, and no occupants.

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Front axle 2150 KG (4740 lb) 40 KG or 88 lb HEAVIER! Rear axle 950 KB (2094 lb) 310 KG or (727 lb) lighter. The weight increase on the front axle is due to the weight removed from behind the rear axle being more than the weight being removed from in front of the rear axle, the whole truck weighs 270 KG (593 lb) lighter. I didn't expect the box to weigh as much as it did, the Trail Ready bumper is really not that heavy, its just a 3/16" steel "shell".


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How much flex does the box have to deal with?

With the box and bumper off, I decided to see how much flex the box took out of the chassis.

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As you can see the box stiffens the chassis a little, I expected to see a little more but I measured 3/4" - 7/8" of flex, so roughly 1/8" - 3/16" of overall flex over a 10'2" span (measured diagonally). Not really a whole bunch. I decided not to utilize a 3 point of flexible mounting system, but rather put a little of stiffness back into the chassis, just like the box did, just like the factory accommodated.


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I designed a mounting sill to fit the factory mounts, I wanted to keep the floor of the deck as close to the factory box floor as I could, the sills are 3/16 50W steel with windows cut for shock and frame component clearance, all windows are capped. With a 3" crossmember and enough vertical wall in the sill to retain integrity, we are within an inch of the factory floor height. I also took the time to CAD a rear bumper that incorporated the hitch. I have designed a few certified class 5 hitches, so I basically robbed the design, but with the skinny rear frame of the Dodge I used 2 shear plates per side out of 3/16 rather than 1 out of 3/8 which is typical on the heavier builds. This grabs the rear of the frame the way the factory hitch does.

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Here is the deck, 2x6 C channel perimeter, 3" C channel cross members, all 1/4" 6061 T6. The deck is covered with 3/16 aluminum diamond plate, 5052, all welded with a Miller 350P welder.

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A good steam cleaning, removed some of the flaky stuff with the wire wheel, and a quick shot of chassis black made it look like new. I was surprised at the condition of the original paint, especially with our corrosive winters. A new set of pro Comp adjustable shocks will help tune the ride in.

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I decided to redo the rear bumper, I upped the shear plates to 1/4", bumped the hitch tube side from 3x3x.250 to 3x4x.250 for a little better look. I increased the height a little to balance out the look and keep things centred. I also increased the size of the license plate box and mounted the trailer plug inside and beside the plate to keep it protected. Powder coated the sills carbon black with a primer under coat, the deck was powder coated silver and cleared to match the paint on the truck.

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On with the deck!

The sills are drilled to catch every crossmember. 4 1/2" stainless bolts grab every crossmember. The sills are held to the factory mounts with 5/8 grade 8 bolts and stover lock nuts, overkill for the application but they fit the stock holes nicely. I hate grossly oversized holes and flat washers to compensate, I prefer a higher degree of accuracy. The side sills of the deck are cut out 2" for tire clearance and trimmed with a 1/4" aluminum "flare". I initially was going to use 4" sills but I needed a little more cross section to accommodate the fuel filler, and assist in mounting locations for the cabinets that will be bolted underneath.

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Some details:
The headache rack is a bolt on, can be made to accommodate individual needs, The "shoes" are wheel chocks and tie down points for bikes, the headache rack and wheel chocks are all 3/16 aluminum. The whole assembly is 2" thick, and the headache rack is only a 1/2" from the back of the cab, maybe a little tight, but the deck has an extra 1/2" of front to rear adjustment built in so I can slide it back if need be, it will keep the camper tight to there back of the truck while still retaining a headache rack, I like thew safety and security with that design. The headache rack is gusseted back 6" on the lower end for rigidity, the camper will be snug in that part but again, positive retention and strength is the key.

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Bumper details.

Just some bumper details. The tow lugs are designed for a shackle and a hydraulic motorcycle lift at the same time. If there is any capacity left I will try to set it up to carry at least one MC, The lift is being designed to utilize the receiver and be stabilized off of the tow lugs. We usually always drag the trailer out as it is fully equipped with gear, fuel, tools, spares, and behind any of my trucks it's not really much of a load, plus it's a great shelter if the weather is ugly. But I've always wanted to build a really cool MC carrier!

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The rear wings are fully capped with a drain hole at the bottom, it will get in, might as well let it out! 3 5/8 grade 8 bolts on either side hold it in place.


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Dual shear plate design.

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How's that for a colour match, 11 year old silver paint and fresh powder.

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All wiring and lighting is enclosed in the rear bumper, anything over 76" wide in Canada requires all of the clearance lights I have installed. Generally you can get away without it in a private vehicle, but I've been pulled over more than once by somebody who didn't know what the actual rules and regs were, so we will go with Transport Canada commercial specs for lighting. Avoids wasting my time later.