Here's the promised pics.

Getting ready.





Hatch removed.





Out with the old.





In with the new. I have enough room in front of the new tank for a 10 - 15 gal fresh water tank. (winter project)





I used "Great Stuff" window and door foam, it said that it stays flexible. I ran beads from the sides toward the middle, leaving space in between for it to breath and allow water to run out if any finds its way in. Then I put a couple of globs, one on each side to help hold it, then I strapped it down. It seems very secure, we will see.