I remember a fuel tank repair from back about 30 years ago. Used to be an auxiliary tank maker called "Travel Accessories" in NorCal. One of the welders did repairs in his free time.

He talked about someone bringing in a leaking 20 gallon aux tank. Said he didn't get all the gas out before taking the torch to it. Gave the owner back his 40 gallon tank.

I guess my point is that some things are best left to professionals. I like the radiator shop idea.