I just realized I never finished this post so here is a long overdue update.
I used 5200 to seal the screws that are holding down the coffin cover. I knew if I used 5200 for a seal it would have yellowed and I'd never get the lid off in the future. I ended up using a marine grade white silicone and so far I'm happy with it. It's holding up good so far. I figure if the silicone starts to loosen up I can peel it out and re apply some.
Here's a few pics of preparing the floors and installing the cover....
I decided to add a couple of stiffeners on the bottom of the cover. I glassed on two pine 1 x 2s and then put a few layers of glass over them. Here's a pic of them under some weight when I first glued them on. couldn't find the pic of them with the glass over them.
Tank in and finishing the repairs and paint on the lip around the coffin and beginning to paint the floors:
pics of the floors with paint before covering up the tank:
Test fitting the cover.. lookin good!
Caulking up the seam. This first part was done by putting down a bead of caulk and smooting it with my finger wetted with water... I didn't like the edge so I did the rest by masking off then putting down a bead and smoothing it. much better.
more caulking:
All sealed up!
Ready for fish!