Sounds like a one off use then Chris?
PVA has never failed for me.
I'm no expert but I think waxes are more for moulds you are going to use repeatedly, where you can build up a decent thickness of release agent to a high finish.
PVA has been quite forgiving for me.
Bear in mind though it's a different PVA than the White glue used for woodwork. Using that might have the opposite effect desired!
It's blue and sort of smells a bit like french polish.