[BrianG]

Wow, a 12v true heat gun would suck some serious current. Most 120v ones draw ~10-15A. That is between 1200 and 1800w. To get that power at 12v, you'll need 100-150A! The best you could hope for is to get a 12v hairdryer. Or, use a 120v extension cord (but make sure it uses 12-14GA wire because of the current).