Hey G-19...
The mold that I have is 0.06" wall thickness. Once the gelatin has set up in the mold for 24 hours, I will take it out of mold and place it back in the refrigerator, sitting on top of the mold. With this wall thickness, it can support the ~25 lbf weight of the block without any bending of the mold, etc. So it seems tough enough .
Tom