The more I think about the freezer thing the more problems I come up with. Just common sense here but
1st you gotta have a freezer with enought room to put the gas tank in
2nd you gott a fill it with water and seal it "water tight" or it will just leak out before freezing
3rd seems like if the ice was strong enough to pop out the dent it might also distort the whole tank
When my b/f
characterized his tank he was told there is a tool that goes inside the tank to push the dent out, then a little bondo touch up, repainted, now looks good as new.
btw Guitarzan......... just how much character does your Savage have?