I did a similar thing but used just enough epoxy to fill the gap then later when the deck was finished and the hatch holes cut out, I was able to sand the seam then lay down more glue and tape.

re. you mention another layer in order to make the seam stronger, it would probably work better to think of adding glass and resin to make the joint stronger, it takes a lot of resin to connect to pieces of plywood together, thats what glass cloth/tape is for.