I have never tried this but I bet it would work on some dents. The heat gun goes to about 200 deg and then the can flipped upside down cools the metal quite rapidly to below zero. The premise being the expansion and contraction of metal. The only danger being to the paint itself. Sometimes the paint doesn't react as well.
Sean that sounds like a lot of progress! For what it's worth the truck looks pretty good but there is a lot of work to be done.