Subflooring question!

[reprobate]

I think the 30# felt is a good idea. Felt makes a good moisture barrier that breathes and doesn't trap moisture in the long run. Any plastic will. As for the plywood, OSB or a CD ply both have exterior glues in them. If pretty much soaked Osb will swell esp. around the edges whereas a CD will buckle. Neither of which I would be the least bit concerned with in your application. Just use a sheet good with an ext. glue. Liquid board stretcher (constr. adh.) is great stuff, so use your liquid nails liberally. If you go with a T&G ply, even spread a little glue on the tongue or groove before putting them together. Moisture and squeak stopper. Best of luck.

Welcome back, KC-10

[Ryan Grimm]

Please don't confuse ROSIN PAPER with TAR/ROOFING PAPER.
Rosin paper is used in houses between the ply subfloor and the finished wood flooring. It is a moisture barrier, to SOME extent, but is there primarily to allow some movement of the flooring over the subflooring without noise or buckling.
If you want a moisture barrier, use heavy poly sheeting.

I recommend ataching the flooring (or at least the subflooring) to the bus. There was a report of appliances attached to the flooring and it let go during an accident. This has possibly fatal potential for the driver and passengers.
There's some guy (can't remember name or book titles) that does comparisons on RV and trailer designs, with the intent of developing safer RV designs. One instance in his book was of a VERY pricy RV that lost it's brakes, and when the RV crashed the cabinets let go and crushed the driver.

PLEASE SECURE ALL FURNITURE IF AT ALL POSSIBLE. If the cabinets are attached to the flooring, then make sure the attachments go through to the bus metal as well.