[FishTri]

Never heard of the epoxy sealing; you might want to look into that a little more, in that it could help over the very long term to protect from UV and the foam getting brittle and breaking down. I've seen this discussed as a possibility, but I have never seen a post with anyone who experienced the foam failing over time, so I just did it.

First I cut strips of eggcrate to the contour of the back of the tank and the overflows. Cut them undersized (not as wide) because the foam will expand beyond the edges.

Lay them on a flat surface, with wax paper underneath. The wax paper was great! Stuff peels right off.

Apply the great stuff. I used short (3"-6") strokes on a diagonal starting from the top left of each panel, working back and forth, so that the diagonals ran rising from the left edge up towards the right side. Don't worry about filing in the little squares - the foam will work its way down. Smooth even strokes - like spray painting. Control the width of the foam with the speed of your stroke. It expands like crazy, so I tried to keep moving at a good clip to get the most coverage.

I sorted my shells into different sizes:

Large - A couple minutes after I sprayed the foam I stuck these in on edge to create a shelf. Getting them to stay vertical was a challenge, 'cause they wanted to lay over. A little extra foam on the underside helped.

Medium - after the little shelves were in I "artistically' placed some of the medium shells.

Small/Tiny - then I sprinkled the tiny shells and fragments across the entire surface.

Let everything cure for 12-24 hours. Especially where it went on thick.

Then flip the panels over. I used a blade out of a carton cutter to scrape off the foam that had gone all of the way through. This gave me a perfectly flat back to glue to the glass and overflows.

After the strips are glued up to the back of the tank you can spray foam between the gaps. If it expands too much, pat it down with your hand after a skin has formed. You can work it this way fifteen or twenty minutes after you spray it, and for another hour or so as it cures. Gives you nice flat seams the same height as the pre-made panel on either side.

SPRINKLE some of the Small/Tiny shells on the seams. Just throw it at the seam and it will stick. Otherwise you'll end up with clean seams (no shells) that will look obvious.