Post-curing is definitely the best solution, but you may still get a bit of shrinkage later, especially if the part is a body panel that sits in the sun and might exceed the post-cure temp or the resin Tg. A coating of some sort also helps, though again you will still likely get some shrinkage over time. I find the absolute best solution is to post cure as high as you can, then sand the part flat if it shrank at all, then spray a high solids clear coat onto it, post-cure again to the same temperature, and then do one final flat and polish. This should effectively prevent it completely provided your resin has a decent Tg and doesn't get exposed to temperatures above that. 

Morning folks!