the "flip flop" style, like the thurston james one, isn't good for big parts.
the plastic nearest the hinge can hit the positive form and sticks. the rest of the plastic then stretches unevenly across it. to really make the flip/flop work, i'd say you'd need to have the hinge slide up in addition to flipping over.
the other thing, which is the BIG reason i didn't go that way, is that the plastic sags as it heats, and the sagging gets faster the hotter you go.
with the protoform style, your plastic is sagging away from the heater. with the thurston james one, it's sagging TOWARD the heat source, which has FIRE written all over it.
