I had a similar concern for my background and wound up using a scrap sheet of 1/8'' plexi. I cut it to fit snug against the tank silicone and just laid it flat against the back pane. I probably should have put a bead of silicone along the top but all the gravel, rocks and root structures imbeded in the foam and braced against the bottom have held up for a good 6 months now.
__________________
24''l x 12''w x 12''h 15 gal. - 1x female Leopard Gecko
18''l x 18''w x 24''h 35 gal. Exo-Terra Vivarium - unfinished
and lots of fish
|