When i re did my fishing seats earlier this year i did exactly what you are thinking.
Build a bench seat for boat.
A boat canoe kayak or even a raft without seating is simply impractical.
I used a de stitching tool and dismantled the old covers and used them as patterns for the new ones.
They turned out great and i used this as a learning experience on how to make the bench seat from scratch.
Attach a level to the top of the sheet and shim it to level.
If it s already in the water then problem solved it s already level.
Seating is one of the prime fundamentals of building a boat.
Building a bench seat for your boat.
It might float but staying atop the boat will be difficult.
Items you will need lumber 2x2 inch sufficient to construct deck mounting frames attached to front and back seat fascia plywood marine cut to pattern shown for seating unit side and supporting panels on 24 inch center to center intervals plywood marine sufficient to make front and back.
Just stating what i learned from googling and.
Take a sheet of luan or other thin plywood about the size or slightly smaller than the front of the bench.
Things you ll need tape measure pencil hinge plates drill screws saw marine plywood roll of 1 inch foam contact cement scissors marine vinyl staple gun staples razor blade.