read through the stuff on DonP's website (damn....slipped my mind..."Unconventional Airsoft"?)....and on extreme-fire.com
There's loads of info, much of it dumbed down to mere mortal levels, on those two sites.
There are LOTS of MOSFETS that can be applied to V3 mechboxes....some no bigger than your thumbnail. But I cooked the last little one I had...so really...keep in mind that heatsinks are a good thing.