Anybody not using undercoating?

I'm just doing mine with brush on rustoleum (although my dumbass forgot they make red rustoleum.. i went black out of habit) It's not as pretty as sprayed but is hard as cement when dry. I don't worry about rush proofing or anything, how many of us will ever drive our cars in salt/snow... or even rain ever again? My goal is just to remove existing rust and cover up the metal.
P.S. i'm also just building something to beat the piss out of.. not a show car :)