We purchased an old ('87) Class A RV with the intention of renovating it into a temporary crash-pad to use while we build our main home...never to take it on the road again...
Well, like most things in life, it has turned out to be a bigger project than I had originally expected. Anyways, we've got it rebuilt for the most part and finishing it up...The exterior looks horrible though and cost for new RV siding is ridiculous - I'm wondering about furring out the exterior walls and applying cob/plaster...it'll then match our future structures...
You can do that but you will want to use a sealant over the whole RV prior to adding the cob.
This is so the moisture in the cob won't start to deteriorate the RV by moisture infiltration.
I've seen it done up in the Ozarks and the guy used A sealant designed for concrete blocks, he used a roller to apply two thick coats of the sealant then he attached window framing around the windows and caulked those, then he attached expanded wire like for plaster with small standoffs.
When I saw it, he was on his third side of the Old Trailer he was turning into his home.
We thought about doing something similar with a Fema trailer we are now using for storage but I planned on putting up a complete frame with foam board insulation on top of a sprayed on sealant coating. The outward progression was going to be: trailer sides, sealant sprayed on, insulation boards glued to the sealant, wood framing with expanded mesh to hold the cob in place. When we checked our soil for suitability, it was going to take to much amendment to make it worthwhile so we scrapped that idea and haven't gotten around to working on that problem anymore as of yet.