In Bed gas filler issue

[Orence1]

Putting together the oak bed in my 72 LWB. Using the LMC tank with the center fill neck. My issue is the clearance from the bottom of the bed board to the filler neck. In the picture you can see the dimensions. I have 3/4" (Arrow B) from the top of the filler neck to the bottom of the board, 1 1/2" (Arrow C) from the top of the filler neck to the top of the board and 3 1/2" (Arrow A) from the top of the tank to the top of the board. I originally was going to use the round marine style filler that had a screw in insert that you use the key to open. Not enough clearance for that. My current thinking is to install a billet flip up fuel door and cut a hole in the board above the filler neck. Where I am stumped is to how to set up a gas cap with the clearance issues I have. I have seen some pictures of wood beds with a similar set-up but they all show the flip up door and no close ups of what is inside the door. If any of you have any ideas as to how to set up a gas cap of some sort I would be grateful for some direction. Thanks in advance.