To install an AC power outlet on the back of the dummy filler neck, the following modifications are required:
1) Use a 100° countersink tool to cut countersinks in the four holes closest to the center of the clamp plate. The outer diameter of the countersinks should be .385". Use low speed to prevent chatter.
2) Cut threads in the two smaller holes with an #8-32 tap.
3) Use a drill to remove the four bridges that hold in the center plug. Once the center plug is removed, use a curved file to remove any burrs. Apply touch-up paint to the exposed rim of the hole.
Use four #10-32 x 3/8" flat-head screws with a 100° head to attach the clamp plate to the filler neck.
https://www.mcmaster.com/91771A963/
Use two #8-32 x 7/32" pan-head screws to attach the AC outlet to the clamp plate.
https://www.mcmaster.com/91772A872/