I picked this up while replacing the tank in my skiff. The fill cap has a barbed outlet tapped and epoxied into it so I could use it in the front hatch connected to the vent line. A new cap can be purchased for a few dollars. Still in like new condition- https://www.westmarine.com/buy/west-marine--12-gallon-tall-profile-low-permeation-above-deck-fuel-tank--13854229?recordNum=2
$60 located on Folly, but can meet anywhere around town