The tank can easily be drilled and then the nylon rod embed into some thickened epoxy, and not a chance of a leak. I was considering using egg crate as my plastic backing, an attaching the rock by zip tie, and before foaming taping the back of the egg crate off with packing tape, and securing the structure also down to a flat surface to keep the panel flat while it hardens, and the detach is from the framing board, and at which time I could remove the packing take keeping cleanup of the back side to a minimum and flat. Before trimming and fillin in with sand is when I'd drill the panel to mate up to the nylon rods, and would have to work on hiding the washer an nuts...