As you know, the gas tank is behind the seat.
The tank sprung a leak while driving; my brother is driving here to Knoxville from Charleston.
Are there any products available at auto parts stores to use on a wet area that will seal it?

Tell him to go to Walmart and buy a 6 gallon gas tank and fuel line for an outboard motor and put it in the bed of the truck. He should be able to fit the line in the parking lot. Oh yea, and Id pull the stock tank out and throw it in the bed too. Make sure you tell him not to lite up a smoke. And Walmart could fill the tank too.

That, or siphon the tank down below the leak, then dry and clean it and mix some two part epoxy. Just beware that if it's rust, you'll be back in there again when the next pin hole starts.