When I was 17 I stripped my car with something called Aircraft Stripper. Worked great but a fair amount of time to get it all off (the paint). The car did have 3 coats of paint at that time, so I'm sure that did not help. All I remember is the fumes were not great and the stuff burns like hell if you get ANY of it on your skin.
He tried the "Aircraft Stripper" brand and it did an okay job.
He is currently using the "Rustlolium" brand aircraft stripper and it is wroking well.
Will remove almost all the paint and softens up any bondo on the body.
Neutralizes on it's own after exposed to air.
Also been using the aircraft gel for years but recently have gone to Easy Off oven cleaner for parts. While the Gel is hard on your skin the oven cleaner is just deadly wow. Do not breath this crap in. It works extremely well though.