Sprayed my (wife's) 1993 Jeep Wrangler inside and out with a schutz undercoat gun, supplied by ML. I used the OD Green Monstashades (colored ML) and it turned out sweet. Four gallons is best to go inside and out a full three coats but I covered the rims, flares, etc. with that much, so most people can get away with three gallons in my opinion. The Schutz gun took some getting used to but worked well once I realized that I needed to tune in my pressure AND adjust the tip--if the spray tip is too closed, it starts to collect and then makes clots that come out like...well, I won't get gross here.