I would think that the plastic would have a tendency to trap moisture against the wood. Which would obviously promote rot. Though a sheet of plastic between the carpet and plywood may prevent the carpet from holding moisture against the wood. Personally though I would stick with sealing and...
Welcome!
If you could find a foot control trolling motor cheap you could mount it up front, sit on that middle bench and steer the boat with your foot.
My dad has a 1436 that we put a flat floor in by laying foam between the ribs. Then we glued plexiglass to the foam and carpeted over the plexiglass. We have had this floor in the boat for almost 15 years. Might be a good lightweight option for you. Plus it makes the floor removable. I believe...