68 c10 fuel tank problem

[fireman68]

Hi all, newbie here. Getting read to start my first frame off restoration, well first restoration ever for that matter. I have a 68 c10 driver and im having issues wit the fuel tank leakig. What's happening is with temperature changes the tank is pressurizing itself and leakin a little bit of fuel behind the seat where the fuel line connects to the sending unit. When i remove the gas cap i get a rush of air and a face full of gas fumes. Im a firefighter and i know how dangerous this can be in a inclosed garage which is why i have moved the truck tk my detached garage away from ignition sources. Im at a loss as to what to do about this, any advice? Thanks.