Technical Can you seal a gas tank...from the outside?

I used silver solder on a pair of Indian tanks for pinholes. Where the steel was too "lacy" I silver soldered brass mesh cloth over it. Then I internally coated the tank with a tank sealer, and bondo'd and finished the exterior. Its still "fine" altho I intend the cut out the bad areas and replace with new steel someday.

 

Back in the 90's a Racoon hit my Chopped 37 Chevy as I was driving on an express parkway. We heard it banging the underside of the car as I passed over it. The next day at a car show I spotted pieces of Racoon fur on the tire rim of the wheel he ran into and I also smelled gas. The fuel line fitting near the bottom of the 37 tank was wet with fuel all around where it was soldered to the tank. Removing the tank would be a pain since my tail pipes and part of the exhaust would have to be moved. I decided to try a temporary fix and used an epoxy putty in a tube similar to the FastSteel I currently have. I jacked the car up on an angle as much as I could hoping the gas would not be near the leaky fitting. I cleaned the paint and any coating I had on the tank, sanded the area good, rolled the 2 part putty in my hand mixing it until it started to get warm, wiped the area with a rag and spread the putty firmly around the fitting. When I checked on it a couple hours later there were no leaks. I put the car back on the ground and checked it again the next morning and saw no leaks. Did a little sanding, some repaint and drove the car until 2000 when I sold it.
This thread got me thinking because I bought that 37 Chevy back in 2011 and guess what, that tank with the epoxy putty repair is still in the car with no leaks. As far as the Racoon, my buddy driving behind me in his rod saw him as he exited from the rear of my car and did a final number on him as he ran him over with his car.

 

Yep, I had fibreglass tanks in two of my boats. The last one had an aluminum tank, and it would make sense to me that it was because of the change in the gasoline formulation.
Bob