Couple of Box Build Qs

[dzzz]

1) Is marine plywood a suitable material to lay on a box frame? Has anyone put sandwich fiberglass directly on the frame?

2) What kind of insulating foam board should I use in the floor?

3) Aluminum I beam v. traditional steel square tube. Your thoughts?

[FusoFG]

1) Is marine plywood a suitable material to lay on a box frame? Has anyone put sandwich fiberglass directly on the frame?

2) What kind of insulating foam board should I use in the floor?

3) Aluminum I beam v. traditional steel square tube. Your thoughts?

I think plywood is too heavy. 3/4" plywood weighs about as much as 1/16" steel. And probably 3 times as much as 1/16" aluminum.

I don't know what sandwich fiberglass is.

My first Fuso camper was 1/2" and 3/4" plywood covered with fiberglass on both sides. It's a standard truck body material called FRP. It's even heavier than plywood alone but it's more rugged.

Blue or Pink foam board not white for the floor - same for the walls and roof. Urethane sounds better but it absorbs moisture and ends up heavy and not as high R value.

Either aluminum or steel is fine for the frame. Aluminum is more expensive and although it's lighter than steel, there isn't much material in the frame so 14 - 16 ga steel tube doesn't present much of a weight penalty.

I think prepainted aluminum panels glued to a sq steel tube frame (14 ga floor, 16 ga walls and roof) would be fine.

That's how my second Fuso camper is made.

[R_Lefebvre]

3) Aluminum I beam v. traditional steel square tube. Your thoughts?

Assuming you're talking about the frame...

No matter the material, building a frame with I section instead of square tube will be more difficult. Just because of the way the sections come together for joints.

Aluminum vs. steel.... I considered building my trailer out of aluminum. But, steel is easier to fabricate, unless you're set up with all the aluminum fabricating tools already. Aluminum is soft so one would think it cuts better... and it does... but it tends to gum up saw blades. Steel can be cut with abraisives that are cheap and don't clog. Same deal with shaping. Aluminum is done with a file, or rotary hasp, which clog up quickly. Steel can be done with cheap abraisives. Welding steel out of position is easy, aluminum, not so much. Bolting steel is easy, aluminum requires much more care due to it's lower strength. Where one large bolt could support a load in steel, with aluminum you need to make the joint with multiple smaller fasteners to spread the load on the joint.

[dzzz]

By "sandwich" I'm just referring to FRP panels with foam or honeycomb in between. For the floor I want to do aluminum, then foam, then FRP.

I don't plan on the camper being removed, but I am thinking about how it would be removed if necessary. Somewhat of a modified flatbed build. The frame and camper will have wheel wells, but the resting wheels do not extend into the wheel well space. The "flatbed" floor is just the steel frame, with the aluminum sheet being integrated into the camper. My concern is how thick that aluminum sheet needs to be. I could put plywood against the steel, but I don't want to keep adding material "just in case".

My plan is to build in my garage and place the body on the truck with truck camper type legs/lift.

From my perspective the ideal shell build is to be able to order sheet material (FRP, foam, honeycomb, decorative plywood, etc) and assemble structural wall panels on site on a horizontal surface. Windows would be cut and attachments could be added. A system similar to frame house construction in North America.

For example, I would want the full thickness of FRP truck panels on less than half the surfaces.

Those of us needing significant insulation benefit from thicker walls, since with structural panels the resistance to deflection increases with the cube of the thickness. Maybe we can get an engineer to model a cube, allow changes in structural wall composition.

[Stan]

I am just starting the build of a box on an MAN 8.136 ex Danish army 4x4 lorry.
Origionally i converted the insulated tarp used by the army but now due to heading off for a year am doing it a little better. See the old set up here http://www.theoverlander.org and go to 'my wheels'

Now we are making a box 4mx2mx2m out of 40mmx40mm stainless box section, the outside will be clad with 1.5mm aluminuim sheets, the inside will have 28 mm kingspan insulation and the interior will then be lined with timber or ply where its not seen..The idea being its quick and easy to make and maintain on the road. We are having to use stainless box due to the reaction of aluminum with mild steel (like on landrover door bottoms).
Hopefuly the construction will be straight forward.. we start on monday..

Cheers

Stan

[dzzz]

I will look at your pics. A couple of sacrificial anodes might take care of the steel/aluminum problem and save a few bucks.

[Jeep]

You might want to consider polyisocyanate board insulation. I have seen and experienced foam board insulation "crumbling" if it can shake around at all, this was on coach conversions that seen pavement only. Some sheets were 1/2 gone and the bottom of the wall cavity was full of powder (big powder). If you use foam board bond the sheet to the wall or floor to prevent movement. We have some off highway equipment with foam board insulated cabs that are holding out OK due to bonding the foam board to the outer wall.

I am building my entire frame from aluminum box and rectangular tubing, most likely Kemlite reflections FRP bonded to the outside, Kemlite reefer roof on the roof, Kemlite underpan on the road side. Check out www.cranecomposites.com the FRP can do entire sides with one piece which appeals to me. I have samples of Kemlite, Alucobond, Dibond, and am testing bonding with Sika flex, VHB tape, and a solvent based adhesive from Faucher Industries that is specifically designed for panel bonding and used in the truck body industry. The solvent base lets you be a little less concerned with surface prep. The Alucobond and Dibond are very rigid and impressive in the strenght department, the 4x8 sheets are a turn off for me. If you have any info on annodes I'd be really interested because corrosion carries a slight concern. I'll be using 3/4" plywood for the floor. I'd love to build mine with composite panels but for me the cost difference is too high.


When working with aluminum, carbide tipped circular saw blades work well, routers work exceptionally well, it can be sanded and worked very easily if you lubricate the cutting tool. We use a wax stick called Edge Lube made by LPS, looks like a tube of grease but is a tube of wax. Use a sanding disc intead of a grinding wheel and wax it, very smooth and very fast, the wax eliminates clogging and galling. A 7" 100 grit sanding wheel will remove material very fast and leave a smooth finish. All of our metal tools with the exception of carbide burrs can be used on aluminum with some lubrication (wax in my case). You'd be amazed how fast you can cut a pile of material with a compound miter saw! I'd use tubing rather that I beam, corners and edges are easier and use less material, channels work good for wall "studs".

Hope this helps, I'll post up some pull tests for the bonding agents/materials when I do it, should prove interesting and very real world.

Cheers,
Mark.

[FusoFG]

You might want to consider polyisocyanate board insulation. I have seen and experienced foam board insulation "crumbling" .

I think the polyisocyanate board can asorb water and lose it's R value.

"White" expanded styrofoam board that looks like it's made of beads can crumble badly.

"Blue or Pink" extruded polystyrene doesn't absob water or crumble.

Bonding it to the exterior walls keeps it from squeaking should it move.

Tom

[Mickldo]

I am just starting the build of a box on an MAN 8.136 ex Danish army 4x4 lorry.
Origionally i converted the insulated tarp used by the army but now due to heading off for a year am doing it a little better. See the old set up here http://www.theoverlander.org and go to 'my wheels'

Now we are making a box 4mx2mx2m out of 40mmx40mm stainless box section, the outside will be clad with 1.5mm aluminuim sheets, the inside will have 28 mm kingspan insulation and the interior will then be lined with timber or ply where its not seen..The idea being its quick and easy to make and maintain on the road. We are having to use stainless box due to the reaction of aluminum with mild steel (like on landrover door bottoms).
Hopefuly the construction will be straight forward.. we start on monday..

Cheers

Stan

G'day Stan

I build aluminium boats (see link in sig line) at work. You will still get corrosion with the stainless and aluminium. Where ever you get two dissimilar metals and an electrolyte (salt water, mud, whatever) you will get electrolysis. We use stainless skin fittings, handrails, etc on our alloy boats but we isolate the stainless from the alloy via a bedding compound of Sikaflex and/or nylon boards/washers. Where ever we bolt something down or can't use the Sikaflex we use Duralac (barium chromate IIRC). Even with these precautions we still sometimes get electrolysis.

Personally I'd be using an aluminium frame (like we do on our trailers we build, see other link in sig line) so you are only using one type of metal. To fasten it all together I'd weld the frame and glue or tape the panels on.

[Stan]

Well we have got started on the build.

Got the frame up out of 40mmx40mm stainless box.



Due to the advice you guys have given we have decided to make our own aluminuim and plywood laminate, so 4mm ply glued to 1.2mm aly then glued and riveted to the box section.

Its working well... our progress can be seen here;http://www.theoverlander.org
and go to the 'blog' section.

The door and locker doors have arrived , just waiting on the windows..

will keep you all posted on the progress

Stan