I actually used the heat/cool method on my home refrigerator. I'd bumped it with a chair and put a small dent in it. I didn't use dry ice though. I purchased one of those canned blowers you can use to blow dust out of computer equipment. When you turn the can upside down and spray it, you are actually spraying freon.
1. Heat the area with a hair dryer on the "hot" setting. Do it for several minutes so that it gets really hot. But take note: if you put the nozzle of the hair dryer too close to the metal, the heat will build up in the nozzle and the dryer will shut off.
2. Once the metal is really hot to the touch, turn the spray can upside down and spray it for 20-30 seconds into the center of the dent. If the dent is small enough and the metal pliable enough, it will pop right out. If not, you probably need professional help.
No guarantees, but this method shouldn't damage your paint.
2016 Ford F350 Turbo Diesel SRW 4x4
2017 Grand Design Reflection 297RSTS
2013 Ford F350 Turbo Diesel SRW 4x4 (Destroyed by fire - 8/29/16)
2014 Grand Design Reflection 337RLS (Destroyed by fire - 8/29/16)