here's what i did for flooring in my bus:
I set foam board insulation on top of the stock rubber floor. (1/2" or 3/4", it's been so long i forgot.) I layed 1/4 osb on top of the insulation. pad on top of the osb, then carpet. The flooring near the hot tub instead of pad and carpet has luan then peel and stick tile on top.
Of all the flooring material, the only thing that is attached is the luan and the carpet tack strip. Both of these are just attached to teh 1/4 inch osb.
The walls i also insulated with foam board then i put some really cheap panelling over that and attached both with self tapping screws to the steel beams that run between the windows.
hope this helps
Quis custodiet ipsos custodes (who will watch the watchmen?)