I've been researching building a custom 5th wheel trailer, MDT straight truck, or HDT Motorcoach for several months. What does everyone think the best construction methods are? I've seen welded structural frame with riveted skin, VHB tape attached skin, and epoxy attached skin. I've read positives and negatives of each method.<p>
I've also seen composite wall/roof construction requiring no structural frame. I figure a boat builder in the area might be a good resource for local manufacture since it would be similar to building a boat hull, which must be strong to withstand the constant stress and pounding they take. <p>
Any feedback is greatly appreciated. Thanks.

.....check out commercial trailer manufactures.....there is no more FRP on commercial unites because of blisters from water entering the stack.....Tape jobs are own the way out as the VHB doesn't do well in the sun over time...seems all the new commercial stuff is riveted to steel or aluminum.....RV stuff is screwed and what I have seen lately it is also bonded for weather tightness....though the unite is not built for a long life like a commercial trailer is....maybe 5 year life with the original owner and maybe 5 years up on blocks after that.....the bonded stuff is still out there but why?....it is cheap to build but _does_ break down with moisture from inside and out....A lot of people forget about the inside moisture issue and they rot/soak/grow moldy in usage unless ventilated properly- The Katerina trailers for example.....if ventilated there would not be the problems that they have and each trailer would have only increased in cost by $300 at the most[retail].....every MH/Trailer/TH/or any other unite should have a air to air heat exchanger that is in use when occupied for more than an hour.......geofkaye

Thanks Geof. I thought that composite wall construction might be good, using layers of fiberglass and carbon fiber along with insulation and the appropriate stiffeners, with vacuum bonding if possible to pull it all tight. Thats why I was going to check with boat manufacturers......they are used to building this type of construction for wet environments to prevent water damage.
So you're saying that, in your opinion, the best route would be an aluminum or steel framework with the outer sheathing riveted/glued to it? If I go this route I will most likely use expanding spray foam insulation, which should do several things:
- Provide good R value.
- Seal all seams, holes, etc for a weathertight seal.
- Add additional adhesive strength to the outer skin since it will act as a "bonding" agent to some degree to help hold the skin on.
- Provide good noise/vibration control due to the sealing of all voids, etc.

What is the smooth skin that I see on most trailers? FRP? Is this the stuff you are saying is inferior in the long run?

There are just so many contruction techniques out there, I want to make try to choose the best for durability and maintenance. Thanks.

Hawk Engineering built my shell using 1.5" steel sq tubing on 16" centers, .050" aluminum skins bonded with VHB.
Just for safety's sake, I went inside before insulating and reinforced the VHB with Sikaflex 252 by squeezing a bead down each side of every sq tube.
Sikaflex 252 is used in the manufacture of commercial truck bodies. It cures in 24 hours and once set up, is impossible to separate the sq tube from the .050" alum without destroying it.

Thanks Bob. This is what I have heard from other forums (VHB) minus the SikaFlex. I like that idea since it adds extra strength. I've read about panels coming loose with just the VHB tape used.
How did they handle the seams where the aluminum panels meet to keep them watertight?

Dg, if I may chime in with Bob. The VHB often gets a bad wrap but I believe this is often due to a less than perfect preparation prior to installation. I went through a similar discovery process about all of the skin bonding process before building our coach and learned a few things.

VHB is a chemical process so things need to be done to insure that all is right before you stick-it. Removing any solids and any oil residue along with providing flat mating surfaces is critical to making the VHB products work. And then there’s a “primer” that goes down first with some time constraints on it. No “dirt or dust” present is paramount before sticking the aluminum skin to the framework. When done right it is very durable and will last, but if the builder slacks off you may have issues down the road.

On our coach, Hawk Engineering used a combination of Sikafelx products to seal and bond in different areas of the build, but the bulk of the panels are put in place with the VHB. I was present for a great deal of this process and watched to be sure I understood how they prepped the coach. Our coach is too new to have too many issues like that (I hope) but I have seen trucks and trailers that are 5 to 7 years old with a history of sever duty and they are doing fine. Craftsman Industries that is a specialty builder in our area that uses VHB and has for years with out incident. They also spoke very highly of these products.

The construction and overlapping of the sheets that make up the box are as (maybe more) important in sealing the coach as applying sealers. You want the "seal" to rely on overlaps and gravity when ever possible before the sealers.

I hope another opinion is helpful in your quest.

Merry Christmas, I am going to go open presents with the kids now.

Rad

Thanks Rad. All opinions are greatly appreciated :-) Thats why I am looking into this so much....to get as much info as possible from those that have already done it or have knowledge of the subject(s). Merry Christmas. I looked all around the tree but Santa didn't leave a toter there for me. Maybe its parked outside.....oh, no wait, thats just my minivan. Darn! :-)

I'm in the process of building my own hauler W900L 42' long, 12' slide, I'm ready to start installing siding but I didn't realize there is so many VHB tapes .What tape should I use to attach .050 alum siding to 2"x2" steel tubing
Thanks Jeff

.....contact 3M and get their opinion....surface needs to be cleaned properly and primed for good stick.......also there is a temp dust time and humidity issue that needs to be addressed....geofkaye

Also check out Sikaflex 252. Source: austinhardware.com just type 252 in the search box. This product is used in the manufacture of commercial truck & trailer bodies.
I set up a scrap piece of steel sq tubing & bonded another scrap of .050 aluminum to it aprox a foot long. After it cured, I couldn't separate the them (even with Visegrips) without destroying the aluminum.
If I build another motorhome shell, I would use the Sikaflex over 3M VHB without any hesitation.

Thanks Bob I did some research and I'm going with the Sika
Thanks again Jeff

Got the Sika 252 through Ellsworth Adhesives $6.86 a tube and very fast shipping ,had it in 3 days

Just FYI if you use the Sika 252 invest in a good floor squeege to push the panels tight ,I tried a roller but couldn't get enough pressure to press the panel tight .I would highly recommend the Sika product. I'll try to get some pictures up