I have been approached by a client looking to build a Tiny House on a metal trailer, and she is eager to avoid the use of any foam or other synthetic products in the building.
A recent article in the Journal of Light Construction certainly opened my eyes to the risks of building over a trailer like this, so I am looking for a foam free approach that will minimize the risks of condensation on the trailer.
One of my thoughts is to build a floor system from the metal trailer bed up:
1″ PT sleepers 24″ O.C. to create a vented space between trailer and framing
Vapor permeable Air barrier(Housewrap with taped joints)
1″ Pine board sheathing
2×8 floor joists with Rockwool Insulation in Cavity
Intello vapor barrier
1″ pine subfloor
Does this make sense?  thank you!
Jason MacArthur
Apple Tree Builders, Zone 6