I've done a few major rebuild projects for resale (up to 42') and learned a couple things. Do one stringer at a time no matter where the boat sits. That's the best way to make sure it stays straight. If warped, getting it true later isn't as simple as placing a few jacks here and there...you want to avoid it like a plague or be ready to spend lots of time making jigs and fixtures to make it right.
Stringers...use wood, it's less money
than foam. 99% of the buyers could give a rat's azz whether you used foam or wood for stringers or if you used polyester or epoxy. Few know the difference and those that do won't likely buy a previously wet boat...freshwater submersion or not, resale always takes a hit.
If you want to used pressure treated do a little research
. I've used it on stringers, transoms and floors with great results going on 5-6 yrs . The APA (American Ply Association) posted info on this yrs ago...Pressure treated wood has been used in USA boat production successfully for over 20 yrs with polyester resin. Greenwood Products makes the most commonly used pt wood for boats (CCA process). Old time creosote treating processes were the ones that had a petroleum base that resin wouldn't stick to. Today's CCA processes only need to be dry (the water carrier part) for good adhesion. CCA is the commercial
grade and still legal
in the USA for commercial
use...not residential use.
If you want to do foam, Compsys (preforms dot com) may have them for your boat. They make oem stringers for every big name boat you can imagine and don't do retail. I toured the plant, saw the process and had a production mgr give a show and tell. Stringers are molded to fit exactly and have cloth on them. All you do is set in place and bring resin. If they don't have your specific stringers ask them to sell you a blem or another stringer that you can cut to fit. Blems that would work are ones that are off just enough dimensionally not to meet customer specs. Nothing wrong with them, just 1/4" to low, narrow, etc.
As they say..."Git R Done".