[LynnB]

As far as I know, there is no silicone RTV sealant that is impervious to gasoline.

From the data sheet: "3M(TM) Marine Adhesive/Sealant 5200 is not recommended for use as a teak deck seam sealer. Extended exposure to chemicals (teak cleaners, oxalic acid, gasoline, strong solvents and other harsh chemicals) may cause permanent softening of the sealant."

 

[LynnB]

Nitrile.

 

[LynnB]

It isn't necessary to do an in tank fuel pump. BMW used external pumps for decades on FI cars. For my 83, I use a Walbro pump.
Of course, then you will need to figure out how to plumb a return line. Shouldn't be to difficult. Return line is very low pressure.

 

[LynnB]

Still, hats off to your for your efforts. I have "over engineered" more than one car mod in the last 53 years. If you end up with something you like that turns out to be functional, it is a success; and hugely satisfying.
What we call "trial and error" the big companies call "research and development." The only difference is the budget.

 

[LynnB]

Your car; your choice David.
I would not use it in direct contact with gasoline; especially in this application. If that seal fails in the GT, it will be putting gas fumes inside the car. Most cars and trucks, the tank is more isolated from the inside of the vehicle.
Besides, the MANUFACTURER advises against use where it will be subject to extended exposure to gasoline, among other things. Better off using something that IS recommended for the application.
Just thought the OP should have all the facts.

 

[LynnB]

Someone got up on the wrong side of the bed. No desire to enter into a pi$$ing match. You win if it is that important to you.