Block smoothing filler over large surfaces

Hey, everyone. I'm trying to smooth out the trunk on my 64 Valiant after working out a few dings. I decided the best thing to do was lightly skim the whole trunk with Rage Gold. I've been working on it for over 16 hours now using sanding blocks of various lengths to try and get the whole thing smooth, and it's just making me nuts. Does anyone want to share their secrets for smoothing large surfaces? :banghead:

Thanks!