I have a successful setup for a hidden fuel fill neck. The parts include a late model fuel door from a Chevy or GMC suburban or truch. The two mounting holes will need to be adjusted in closer. This will allow the tow mounting screws to be behind the side marker. No welding required. The next is the fuel neck. The way to go is using a Ford F150 08 or later fuel neck. This is a capless system and will make it easier to fill without the hassle of a cap. The F150 has the right length of pipe and an overflow tub which connects well with the new tank. Just need a 4 inch fuel hose and clamps.
