In assisting our son on the restoration project of his '68 Tradewind, we have stripped down to the frame because the floor was dry rotted front and rear. Now comes the hard part...what to put back in for underlayment that will be as sturdy and moisture resistant as possible. The '68 Tradewind plywood underlayment measured 3/4"thk.
We gave up on the moisture resistant properties because that required chemically treated wood. We were left with
two choices after research with the APA, engineered wood council, (see www.apawood.org
) resulting in a choice between A-C Underlayment or A-B Marine Grade plywood. Neither is treated with chemicals.
The new chemicals ACQ and ACZA will actually corrode metals, aluminum and should not be in contact metal. A definite no-no for the Airstream. (Note if using in construction you will need stainless steel fasteners or double dipped galzanized, not electroplated galvanized either. see www.treatedwood.com).
A-C Underlayment is dense and tight without knots, which is important under resilient flooring, as any compressions or knots will telegraph or show through the vinyl or linoleum flooring. The veneers used are C grade.
A-B Marine Grade is the most dense and without voids, with face veneers of A grade woods. It will react well to movement of the rig, is flexible and will hold best to fasteners. This would be the more expensive choice.
The exterior grade sheathing plywood has too many voids and knots for resilient floor installation.
We are considering painting or sealing the underside of the plywood with sanded side up for finish floor.