Installing a gas filler in the deck, fiberglass
Henry's placement of the filler on the 34 Ford coupe in the lower tank cover... to me.... looks a little 50's Volkswagon-ish. The upper deck just above the deck lid seems like a better spot. So, I found a cool little cap made originally for motorcycles. It's only 2.5" across and is available from Speedway.
Do whatever paint-prep so you have a surface that's not going to change.
Mark out your obstacles and drill a 2.5" hole. Wrap some peel and stick sandpaper around the hole saw and clean it up and make the final size 1/16" larger than the cap.
Make a plug out of wood and sink it as deep as the cap is thick. Hold it in place with a few nails and cover in clear packing tape.
Fiberglass the heck out of the underside. Remember, even though we all hang onto the filler spout while filling the tank, there can be a lot of force on this fitting.
Drill a 1.75" hole for the hose connection and you will be left with a shoulder onto which the filler will rest.
Ta-Da! And... this can be painted to make it almost disappear.
Thanks to my brother-in-law for doing this to his car first and showing me how to do it.