need to insulate between aluminum box and framerails?

jesusgatos

Explorer
I'm mounting a 14ft aluminum Uhaul moving truck box on top of this M353 3.5-ton military trailer chassis, and I'm wondering whether I should use anything to insulate the aluminum box from the steel framerails. The box will be pretty well-supported and securely bolted down - and the trailer only has a single axle, so I'm not really too concerned about the chassis flexing. But should I use some type of contact barrier? Maybe like a thin sheet of rubber or something? Or can I skip it and just set it down right on top of the framerails?

 

ntsqd

Heretic Car Camper
I think that over the long run that electrolysis will be a problem, but if you only plan to use/keep it for a couple of years I wouldn't worry about it too much.
For longer term use/ownership just make it electrically isolated from the steel frame while still making it structurally sound and I'd think you're good to go!
 

jesusgatos

Explorer
Hmmm, I'm not sure how long this thing will last. The trailer chassis is ROCK-SOLID, but the uhaul box has already seen better days (I bought the whole truck for $650). I guess I'll just bolt it down and see what happens. I guess the worst-case scenario would be that I'd have to shell-out another $650 and cut up another uhaul box. Thanks for the advice.
 

jesusgatos

Explorer
But just out of curiosity, what type of material would you suggest using for this sort of application? Thin rubber/plastic strips or wood or...?
 

ntsqd

Heretic Car Camper
Anything with a high dielectric strength will do that part of the job. The structural part in combination makes the choice a little tougher.
Starting guesses:
Acetal ("Delrin", "Celcon", "Turcite"), glass filled would be a bonus
HDPE
Glass filled Nylon
Filon
Possibly even G-glass or E-glass

What you don't want are highly cold flowing materials like teflon or non glass filled Nylon. Even HDPE is pushing on that a little bit. Cruise mcmaster.com and maybe cross ref your choices at mat-web.com to see if it will really do what you want it to do.

Some of the more exotic polymer tapes might save quite a bit of work though they're likely to be more money up front.
 

michaelgroves

Explorer
The main thing is whether there will be standing water around the steel/alu parts that are in contact. If your drainage is good, and these parts are usually dry then the electrolysis will happen over a geological timeframe. If it's wet, and particularly if it's salty wet, then it will happen fast.

Land Rovers, with their aluminium bodies on a steel chassis, used on the wet salted roads of a lot of first world cities, have far more corrosion problems than those used on wet unsalted roads. And in dry climates, it's simply not a problem at all.
 

jesusgatos

Explorer
Drainage won't be a problem. Based on the input here and research I've done this afternoon I think it'll be fine. It's far more likely that I'll destroy the uhaul box in any number of ways before electrolysis will be a problem.
 

chasespeed

Explorer
I would just attach it, with something to seal it well(rubber), stainless bolts...

And locate a few anodes in a few outta the way places... and you will be good to roll....

Chase
 

jesusgatos

Explorer
Thanks for all the input. The box is just about ready to pull off the truck and set onto the trailer chassis. I've got all the hard work done, now I just need to line things up with a shop where I can use a lift to get that big 'ol box up high enough to roll the trailer chassis under. When it's all said and done though, the box will ride within 1" of the height it sits at on the truck but it'll be sitting on 43" tires.
 

michaelgroves

Explorer
I might be wrong about this, but I think stainless bolts through the aluminium would be worse than mild steel (in terms of corrosion to the aluminium). Stainless is higher up (bigger number) the galvanic table than mild steel, IIRC.
However, of course the bolts themselves will be better off!
 

ntsqd

Heretic Car Camper
Something that I've not said, and likely should have, is that if electrical isolation of the box from the trail frame is going to happen that there will need to be insulating washers under either the nuts or the bolt heads, and something the insure that contact can't be made in the insulated side's bolt hole.
If that is done, then what the bolts are made of will not matter. Were it me and I was concerned about electrolysis I would insulate the box from the frame and the mounting hardware.

If you're going to store it on the Sisters - Mt. Bachelor side of Bend (W of 97) this might be prudent. If you're going to store on the Powell Butte - Alfalfa side of Bend (E of 97) then I don't know that I'd worry about any of the isolation, but I would still put some sort of rub/wear strip between the box and the trailer frame regardless.
Salted roads isn't an issue. That part of OR has way too much volcanic cinder for them to consider buying salt.
(I partly grew up in Powell Butte.)
 

jesusgatos

Explorer
So, you'd suggest a rub/wear-strip but not worry about full-on insulation? Here are a couple of pictures to give you a better idea of what I've got going on. I'm almost done welding-in all of the 2x2" crossmembers that run from front-to-back. The floor of the uhaul box is made-up of segments that run side-to-side, so I had to add those crossmembers to support them. The box is going to be bolted down to the four crossmembers that run from side-to-side with eight 5/8" bolts that thread right into the crossmembers on the trailer chassis. I can add more attachment points, but I don't know if it will be necessary.



This is basically what it will look like in-tow (minus the uhaul truck, and the truck and trailer are both getting painted).

 

ntsqd

Heretic Car Camper
Yeah, even if you're not going to worry about electrolysis I'd still advocate some sort of anti-chafe liner between the box and the frame. Doesn't need to be exotic.
 

jesusgatos

Explorer
Alright. I'm going to swap the box onto the trailer chassis tomorrow morning, but it should be pretty easy to jack the box up high enough to slip a layer of something in between the box and the chassis. Any thoughts on something that I might be able to source locally? I have already cut the wheelwell openings, and if I use anything much thicker than about an 1/8" it's going to create unsightly gaps.
 
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