Best primer for rubber/soft plastic miniatures?

I've been away from miniature painting for a while, but I just bought the new heroquest and want to paint it.

The miniatures seem to be made of a weird rubber or soft plastic that I've not used before, what kind of primer works best on these? I'm worried normal primer will just flake off.

Edit: I probably should add, I'd prefer something I can shoot through my airbrush.