Block smoothing filler over large surfaces

Long tools are best for big panels, but if you truly have just a few dings, and the panel was generally straight, I'd take it back down to metal, or close, and just focus on the damaged areas.

Then again, you can always just paint the car White. :D

Seriously, if you're working the trunk lid alone, once you think it's close to good, shoot a little color on it to get a real feel for what you have. I've done it before on separate panels that needed to be spot on.....If I wasn't happy, I just worked it some more. Time consuming, yes, but it really depends on how nice you want the outcome to be.