i used 6061 1/4" aluminum diamond plate only paid $25 per 4x4' sheet off craigslist, each peice had a bent corner from where the guy tore it out, but 5 minutes w/ a hammer & it was flat enough for my 1436's floor.
this 1/4" diamond plate is much harder to cut than wood (i don't have a plasma cutter, only a jig saw & angle grinder), but it's stronger, lighter, & will hold up much longer than wood in a salt water environment plus it keeps my floor lower than 1/2 or 3/4 plywood.
i must say, it looks far better than a plain sheet of aluminum or a piece of plywood. the whole interior will be rolled/sprayed w/ bedliner, the white caulk line is 5200. i used 3/16" pop rivets & 5200 to attach the diamond plate to the ribs, & put wood ledgers against the bench for supporting the ends of the floor then attached to them using stainless screws & more 5200.
for the front, i'm decking from mid bench to front platform using the floor area between them as storage. here's a couple pictures:
the wood ledgers cut to fit
i rolled the wood w/ bed liner before installation, wood attaches to benches, sides, & floor using 5200 on all surfaces + wood to metal coated screws into the bench face
the floor has 1 coat of bedliner on it on it, going to get 2 more before it's finished
haven't gotten the front deck framing goin yet because i'm waiting on the aluminum angle which I ordered Sunday from onlinemetals.com
amazing prices there!
i ordered better material for 1/3 the cost versus Lowe's or Home Depot, google for discount code & got 20% off