I have a 17' aluminum Smoker Craft from the mid 60s. It has some huge dents in it (when viewed from the side with the bottom up it "sags" down about 6" in the center. Some areas have not just dent but folds. If I try to bang it back into shape I am risking damage from metal fatigue. Any suggestions? Pile a lot of rocks in it gradually flatten the bottom?

Put it on the flatest ground you can find (sand beach would be best) get a 4x4 and round the edges on one end some put on some gloves and go to town. I'm not kidding. I fix alum boats daily and you won't fatigue the boat.

Yep, Arcola has this right. Hit it with a 4x4 block to remove any dents. If it cracks just get it welded. Don’t forget to support the other side with something. Outside on your lawn would also work.