Tuned down 2 steps? C Standard?
That's not really that low to be honest dude, not in these days when people are tuning to C below C standard. Other than EQ-ing the guitar at the amp to suit C standard, I honestly don't see what else is needed.
maybe try a tube screamer to tighten up low end. multiband compression. you are probably gonna want a lower end, sludgy sound for a stoner band anyways.
Some of my bands songs are in Drop A. I never had to do anything fancy to make the guitars and bass sit well. Just distort the bass some. That always helped me out.
drop A has been decently standard for many bands from years ago, and yeah there's no real trick to it as far as I'm concerned, just Eq it in the amp the way you like it