Wish I'd caught this thread before you cut her open, as I MIGHT have some tip to closing her. How are you planning to close her up? When I do mine, I expect to do much the same way as when I cut out the floor (deck) of my sailboat a couple years back. Same principle, only the tank is much smaller. Would you happen to have left yourself a 1/2" or so of bottom 'lip' in place, after you removed the bottom? If so, you can 'line' the tank. That is, cut thin, flat plastic, say 1/2" wide. Adhere it in place so that half of it is adhered on the inside flat of the cut, while the other 1/4" projects out. Smooth, nice cuts, literally line the entire cut out. Once in place, and dried, it's then a simple matter of 'wetting' and then dropping the bottom into place. The 1/4" projecting lip will hold the bottom in position. On the bottom piece, just before slipping into place, wet it well along the sides where it will be sitting on the projected lip. Once hardened, voila, sealed tank, no need to pour anything inside to slosh about hoping to cover/seal the cut line. Like I said, exact same principle as opening/sealing with a sailboat. If anyone is interested, to better clarify my point, I can post a 'self-explaining' picture... but it'd be of a boat deck, lol's. ~Gary