I do love your tank and I totally agree that it is nice to have a decor that is a little different than everyone else's. I originally wanted to put silk orchids in one of mine, and I am going to try the red poppies inside the tank instead of just taped to the outside. I started soaking them already.
I have made caves and used aquarium sealant on them, as well as using aquarium sealant to seal off any sharp looking edges on my tank dividers, I haven't had any problems with that at all. Of course I followed directions I found here somewhere, let the sealant dry for 2 days, then soak the item in water for a day or two before I put it in a tank with fish.