Again - issues with shrinkage - that's the work under the product. If you're using a high build to take care of scratches, no biggie, but understand the cheaper stuff shrinks more so give it time to do it before you block it out. If your surface is smooth to begin with, shrinkage won't show any scratches under it. A trick I've used before is sticking the car in my Cover It garage. On a 50-60 degree day it's 80+ in there and it cures the primer faster. It might be cheaper and faster if you use a spray filler, then spend the time and effort blocking that down...