I personally like a flat floor in my boats for many reasons.
I used closed cell foam (not styro foam) which will not absorb water, under my 1/2 inch treated wood with a sand (ruff finish) stain/sealer/paint which gives it great traction. Line or lay foam under floor with any seams going from bow to stern to help any water drain to stern, leave 1/4 gap on sides to also help drain. Affix the floor to the ribs only. You can get the "sand" is packs at hardware that isn't real sand, goes in the final coat of paint. I use Parker's and even put a coat around top for added traction.
One boat is 13 years old with this, never an issei and did not add additional weight to be concerned with.
If your mounting seat pedestal make sure some fasteners are through floor into ribs.
Am sure others will comment, I am not a aluminum fabricator.
It's not just a duck boat, it is a tatical platform for opportunity- weedwacker 101
Preserve game and hunt with a trained dog- NAVHDA
"In looking back thru his posts over there he kind of thinks of himself as the zen of all things fowl."