Re: floor rebuild
I'm using Auruco ACX exterior grade plywood from Lowes at $29 for 1/2 inch and $39 for 3/4, sealed with 3 coats of Rustoleum polyurethane also from Lowes for $30 something a gallon. A lot of guys will use the Auruco and epoxy resin at about $125 a gallon, but that was too rich for my blood. I told my younger bro if the decks rot out in 25 years it will be his headache. My boat will also be stored in a garage every night it is not in use. If I was storing in the weather I would probably spring for the epoxy.
Whatever you seal it with the Auruco seems to be the most popular and cost effective choice for plywood. I know they had a bad fire at their plant so the Auruco may be in short supply.
Treated 2x4s are ok if you don't have an aluminum hull. Treated lumber and aluminum don't get along well, the treated lumber is said to cause corrosion in the aluminum. If you need untreated 2x4s you should be able to get them at a lumber yard for a few bucks each.