I agree with Ralph, the wax is key. When you build your plug or mold, polish it to a high gloss. Before using it, apply several coats of wax and rub it out. The test for a boat mold is a rag tossed down the mold will easily float the full length without slowing down. You may not need to make it this nice but the wax coat is what really creates the release. PVA is good stuff and will make a good wax job release even more easily, but is not intended as the sole release agent.

Your part should just pop out of a well prepared mold with just a little help from wedges.

: The plug over which I built the seat was made intentionally flexible. I too
: had a fun time extracting the seat, but I was able to twist and flex the
: seat and mold together so that I freed the seat incrementally. I had let
: the seat cure overnight on the mold. Next time I think I'll wax and polish
: the mold before applying pva and see if that makes it any easier.

: Ross