I used a product like that on my first truck, a 67 datsun. My Dad and I sealed the gas tank, worrying about rust... The truck sat for a year while we rebuilt the enigne, and yes there was gas in the tank- not so good. The sealer began lifting and coming off in sheets. We eventually cut a big hole in the top of the tank, and cleaned it out, and welded it shut. It was safely done though.
That being said, the fault must have been ours, as airplane guys and gals use it all the time. Frankly if its used in an aircraft, it probably is good enough for me.
