Lastly, don't use PT treated plywood. It's soaked with a preservative that takes months to dry out, to reasonable moisture levels.
Plus the preservative chemicals in the plywood or lumber will corrode your aluminum boat and most fastenings very quickly.
Read the descriptions and specs for what you use before you use it, better yet, before you buy it. The birch ply you used is stated to be for interior use, the rustoleum marine paint says one or two coats of their primer are needed on wood AND fiberglass before the Topside paint.
Plenty of boats are built using polyester and about the cheapest exterior ply available for decks/soles/floors. Plenty are also repaired or replaced using the same materials. Crappy materials used well can easily outlast good materials used crappily. Just about anything will last a "few years", depending on what you mean by few.
a small number, a handful, one or two, a couple, two or three;
not many, hardly any
"there weren't many biscuits, but we saved you a few"
I don't think paint or resin alone will work for a plywood floor as the plywood will check and let moisture in. It won't be tough enough for throwing stuff around, dropping anchors etc. Puncture the waterproofing layer anywhere and there goes the waterproofing.
If it was mine, I would use the plywood Gonzo posted. I'd prep it by sanding the bottom with a 24-36 grit disk, followed by blowing and/or vacuuming the dust away, and seal the bottom and edges with a few layers of polyester. NOT WAXED resin and not Bondo or just about anything from an auto parts or West Marine type store. You can shop online and get just about anything delivered to your door. Attach it to the stringers. Sand the top and apply a coat of resin. Let it cure enough so there is no chance any more resin will be sucked into the wood, but the resin is still green enough so the laminating layer will still chemically bond. A few hours to maybe overnight.
Then I'd roll on a bunch of resin, cover it with some 1-1/2 oz mat and more resin to properly saturate the mat. The mat serves the purpose of toughening the deck for dropped anchors etc, keeping the ply from checking and improving the water resistance of the poly resin.
I might use latex porch and floor paint for the finish, or for a more durable and more water resistance coating, a coat of WAXED gelcoat.
The nonskid tiles you are thinking of are probably a bad idea. If they don't shift around and wear holes through the deck coatings, they'll be a nuisance to clean. You'd have to pick them up to clean them (or dip them overboard) as you couldn't wash all the crap out of them even with a pressure washer. You wouldn't want to leave them down all the time as they would collect dirt and hold water all over the deck, which you don't want.
Usually the texture of the mat and the texture of rolled gelcoat is plenty of traction for a boat. If you want, you can use A VERY LITTLE sand in the deck coating. That kind of deck is easy to clean.
I've never used epoxy, so if you want to use that, the procedure would be different in a few ways, so there's that. No mat, for instance and no wax either, I think.
If the OM used 5/8 ply, I would use at least that. 3/4 would work too, depending on if the little extra weight (10 #?) would be OK. That would be a lot stronger and then, even if it did rot, it would take longer to do it. So, for a few more pounds of weight and a few more dollars for the ply, you might get an extra year or so before it had to be repaired or replaced again.
5/8 ply will have 4 or 5 plys, 5 is better. 3/4 will have 5 or 7 plys, 7 is better. That's not counting face plys that are really thin, like probably on that birch cabinet wood.
Remember about treated wood and aluminum. It can destroy your boat quickly.