Unimog composite camper, should I put rubber between the composite shell and the subframe

[PetitePatate]

I’m currently grinding the box off my Unimog 1300L with the plan of keeping the subframe, next month I’m going to be putting together a small composite box made from 2 sheets of nidacore.
I’m wondering if it would make sense to put some bands of rubber between the subframe and composite box?
Would this help with the vibrations that happen sometimes or am I just over complicating things for myself?

In order to attach the camper to the subframe we are making little fibreglass “legs” on the camper and bolting it horizontally through the subframe. I was considering putting bushings on the subframe at these attachments, but the guy that’s helping me with the composite box says that would not be necessary.

 

[gator70]

I've been going through this engineering. Attaching to the subframe should not depend on composite delamination . I'm not sure how others do it. Raising the inner floor to clear bolt heads and 4x4 steel plates below them should be prudent. Then a grade eight bolts gos through the floor and through the subframe is the engineering. The steal backer plates lay on the composite inside the compartment. After you are finished you can see the bolt heads and the backer plates above the inner surface of the composite. You then need to use wood frame to raise the floor 1/2 " for clearance. The bolt holes should not be the same size as the bolts, a bit oversized. There is engineering data on the internet for bolting composite to frames. Discussing the dos and don'ts. Some folks may say this is over engineering. Consider 70mph side winds on the freeway in bad weather. The habitat is a big sail.

 

[Victorian]

Through bolting the floor to subframe in combination with some adhesive would be my choise for your situation. Best if you have internal floor structure to prevent the panel from being compressed by the bolt.

The proper way would be to bolt the floor to subframe via an internal steel frame member (tap and bolt) to avoid thermal transfer and tripping hazards.

 

[gator70]

The left picture shows exactly that

 

[IdaSHO]

Done right, it doesnt take huge hardware to work and survive.

Our camper is mounted (and designed to dismount) using receivers integrated into the flatbed rail.
The camper side is a self aligning assembly that is bonded/glued and thru-bolted to the camper floor, with a few bolts that also thru bolt into the wall cavities themselves.
Being so low, even all the way down to -20 degrees F thermal transfer hasnt been an issue worth worrying about.

The entire camper is held to the bed with just four 5/16 grade-8 bolts and nylon locking nuts.
On and off the truck dozens of times, and near 40k on this setup already, and no problems to report.

 

[gator70]

The previous post is not good advice for the simple fact most folks won't be able to execute this. Second, the composite panel should not have the core exposed to anything, as it weakens the whole structure. Meaning any cutting away of skins is a bad idea. The weakness in composite panels is delamination.

 

[Ozarker]

Interesting, but @IdaSHO has a second.

Any licensed, PE's on this thread, anyone who can put some proof of engineering knowledge in their opinions?

If I hear anyone mention "thermal bridging" on this site again I'm going to puke!

Rubber has always worked for me and it never hurts.

 

[rruff]

I’m going to be putting together a small composite box made from 2 sheets of nidacore.

Some detail of that would be helpful...

 

[mog]

There is no doubt why less and less knowable people post on this forum.
You can post a suggestion that has worked for years and years, 40,000+ miles in all temperatures and there will be someone that will tell you that is a bad idea and will not work. Of course without providing their 'perfect suggestion'.
Perhaps the reason some people complain this is becoming a 'For Sale' forum only?

 

[IdaSHO]

View attachment 831026
There is no doubt why less and less knowable people post on this forum.
You can post a suggestion that has worked for years and years, 40,000+ miles in all temperatures and there will be someone that will tell you that is a bad idea and will not work. Of course without providing their 'perfect suggestion'.
Perhaps the reason some people complain this is becoming a 'For Sale' forum only?

Indeed.

All the while....

I've been going through this engineering....... I'm not sure how others do it.

 

[gator70]

Other opinions above-
As I said, the attachment points described that altered the composite core by removing the skin would never survive theses conditions.

Santa Ana winds – common - Interstate 10 Whitewater to Blythe

 

[IdaSHO]

Opinion-
The attachment points described that altered the composite core by removing the skin would never survive theses conditions.

You are the only one talking about removing any skin.
If you are too ignorant to realize how such a simple bolt-thru assembly can be fastened without removing skin, I cannot help you.

BTW, this was 2 weeks ago.... And a few days after this we had near 50mph cross winds that rolled multiple tractor trailers.
All the while ours did fantastic. But hey, I'm sure your extensive "engineering" proves otherwise.

 

[Madoxen]

On my Unimog 1700l I have mounted the còmposit box onto the subframe with insertion rubber between the metal and composit. Also when i had the panals made i had fiberglas shs (box section )built into it with 8mmx50 flat bar glued in that and filled with foam it was then drilled and tapped for bolts when were loctighted and spring washered in. .
Hope this helps the OP