Well, it took A LOT of homework and searching, but we FINALLY found an all organic, non-toxic, no VOC wood stain. We used this on the underside and up the sides and top edges of the sub-flooring to waterproof the underside of the trailer and keep any moisture from creeping up. We'll also use this same product to stain our siding once we get the exterior walls up.
Smells a bit like canola oil, but that's it! No stinky fumes!