It appears you are attaching this to a glass background. If you have the oppertunity or end up re doing it again I would replace the glass with ply. You can anchor the foam much better and use a combination of dow foam and great stuff to stiffen up the design .I ended up applying around 5 coats of the floorleveler to my trerrerium and it held up and was very rigid wit 2 blue trees for 2 years.I also sealed it after the concrete was dry. It now holds a green ig that is around 24" and has not failed as of yet. Looks good so far and good luck.Seth.