I play stoner stuff with a VC-30 and a straight boost pedal. Grab the Metal muff and guitar and give one a rattle in your local shop. You may be pleasantly surprised. The gain will be there, hopefully, although a cheapo eq pedal in the FX loop might help with chuggification.
For myself, I'm using the 2x12 VC-30, with a 1x15 out-of-a-junk-shop bass cab as an extension cabinet, behringer boost (a whole 15 quid), and it really gets that early-sabbath tone, going right to Kyuss type crunching death with more boost.