Need suggestion on how to "fix" this problem.

Pulled the carpet out of the boat in prep for installing sheet vinyl decking. One area on each side of the boat is being a problem. The problem being where horizontal ply meets vertical ply and the joint has separated because of the foam that fills the hollow box formed by the ply has expanded and forced the corner apart. Grrrrrr.

Here is a pic of the area in question. The carpeted section below the speaker has had the carpet removed. The horizontal ply has bowed and shows a 3/8-1/2" gap in the center where the flotation foam forced the horizontal piece up. The ply was stapled together with 1.5" staples and glue. I don't have a pic without the carpet, but you should get the idea of the situation from the pic below.

I wanted and expected to put down one single piece of vinyl wrapping around from vertical to horizontal, but because the top piece is bowed, it wont work due to vinyl "puckering". And I think the ply has been in this shape since 1985, so it won't easily be forced back to flat.

Any suggestions on how to fix this or deal with it? If you look closely, you can see the corner edge has a slight bow to it.

Re: Need suggestion on how to "fix" this problem.

The ply is prob 1/2" so it will go back down using screws. Removing the surplus foam will be fun. I'd use a long wood cutting blade for a reciprical saw (sawzall). Patience and a shop vac will be needed.