I've been thinking about doing this over the winter as the parts I can find online seem to be in the $100 range for the gas line and the outside filler.
our boat is like yours in that the tank is blow molded and capped off for it and know it was an option.

I've drilled in hulls before to add more drains/vents but for some reason I'm second guessing this one but I think it's due to the filler being in the middle of the metalflake and if I jack it up, that's a spensive gel repair.