Fender Bunks

Finally got to getting my fenders off, body shop is redoing them, and I want to replace the wood/carpet. Any idea what thinkness would they used, it is off a 98 ranger dual axel trailer. When put my calipers on it, it measures out between 1/4" & 3/8" which is not available in pressure treated. So what type of wood should I use, just regular plywood? Seal it with something? Thanks for the help

I just replaced one of mine on my '96 - from what I can tell they did not use P.T. plywood. If you are worried about rot then just put a couple of coats of polyurethane on it before you glue the carpet on. I used regular 3/8" plywood.