I guess it would have been helpful to explain why it failed.
I created a mold using a 3d printer, but forgot to make any provision for releasing the liner from the mold after it set. So I damaged the liner whilst breaking away the mold. I have made a new mold which is split down the middle and bolted together. I will let you know how it goes.
Dip molding sounds like an interesting thing to investigate though, I will be interested to hear of the results. I imagine experimenting with the shore hardness would also be interesting, there is probably a sweet-spot of hardness vs strength needed.