If you have the time, remove the bench seats and any top seat mounts that is easy to get off. Usually the bolts go through the wood flooring and the nuts are on the bottom under the boat so it helps if you have two people. Rip up all the carpet and just use a good stiff scraper to remove loose adhesive and carpet. You really don’t need the floor perfectly smooth just no raised areas as the carpet will cover minor imperfections. Bad areas, you can use a sander and smooth out. Apply the adhesive with a square notch trowel like you are laying tile. Work in small areas as you go so the carpet does not get to hard to move. Make sure to leave extra carpet on all the sides and just cut off the extra. If you come across soft wood now is the time to replace the plywood. Good luck and feel free to p.m. if you run into problems.