I made some timber molds to contain the Nurture silicone liners - the log mold and the tall and skinny. I used 15mm external grade plywood (because I had it) and some 6mm ply (because I had it) to line the lids so they sit on top of the mold and stainless steel screws. I probably went a little overboard with the screws as I glued all the joints with polyurethane glue as well. I finished it by rubbing it with a cloth spar marine varnish in a very thin coat with a cloth. The most important thing was to have the inside dimensions perfect to fit the liners with no buckling but with good support.