Thanks to everyone for the leads. I will be steering away from the OSB and plywoods for now. The whole idea is to use a material that does three things (if possible).
1. No off-gassing
2. Relieve the trailer of some of its original weight
3. No floor rot.
I may have a way to get around the off-gassing by detailing the floor assembly in a way that seals the outside air from the interior above the sub-floor. But, that is gonna be alot of work with a rivet gun.
1949 Spartan Mansion (30')