I am installing a shower base on a concrete slab. Do I need to set the base in thin set or can I just set it on top of the slab and nail it to the wall studs? The shower base has foam underneith it for support.

If you're satisfied that the foam won't sag or compress over time then you may install it directly on the slab. If you have any doubts about the foam then I would puddle mounds of mortar or cement under the base and drain for added support. Good luck, Tom