This is no longer the case.
While chatting up Bill at the GW store, Dewey, one of the NOVA OPEN gurus, introduced me to some magic casting stuff appropriately called Merlin's Magic. In a fit of total awesomeness, he provided me a few scoops of the stuff to experiment with at home. The stuff is just awesome. I managed almost no bubbles in my casts, and the stuff turned out to be really durable One obvious mistake I made was to not wait long enough after casting before removing it from the molds.
In terms of painting, the stuff really seemed to soak in the paint. When I intentionally chipped the edges, the soaked in painted covered the damage well.
Merlin's Magic is great. I can't wait to use it as a base for some desert base designs.
How cool would it be for people to be able to experiment with Merlin's Magic at the NOVA OPEN? A great little hands on session where people leave with casts of terrain would help out gaming tables all over the place!