I am just about done rigging a 1648 Jon Boat. For a floor I used 1 1/2″ XPS rigid foam between the ribs to level things out and to create even bearing for 1/4″ plywood to keep the weight down . Thats all you need for thickness with the rigid foam between ribs. Then I used Neo Mats from Styx River in a walleye fishoulage pattern that is 1/2″ thick that quiets the boat alot and is comfy to stand on and looks cool for a jon boat. For the front slope the 1/4″ plywood conforms alright and I will put a net mesh across that area for storage. I really wanted to keep the boat light.