I like to use a rubber strip on the bottom of my form...Im not sure what kind I have but I've used them many times and they have not dried out. I've also used cork (gasket material) from an auto parts store. That really works well, but if you happen to get epoxy on it forget it. And finially, I've made some with nothing at all...just a clean, smooth form (formica or glass). I think you could easily get by just using the aluminum.