[SCOTI]

You could source a 'remote' fuel surge tank that are available for retro EFI set-ups.

They are a small remote mounted tank w/a high pressure fuel pump in it that feeds the EFI supply/return. To supply the surge tank, you can use your old school mechanical fuel pump (it basically becomes a transfer pump). The high psi pump then picks-up the fuel transferred over @ low psi & sends it to the throttle body @ the correct/required psi.

Or.... There are many aftermarket in-tank solutions for rear or bed mounted tanks.

The 'behind the seat' tank w/an 'in tank' pump can be done but I don't know of any 'kit' to get it done. Keep in mind if you opt for that you get to listen to the pump if you're wanting that. Many opt for an inline external pump under the cab & add a return line to the tank (again, no 'kit' that I'm aware of).