Stepside rear fender replacement question

[Weasel Diesel]

My 86 SWB stepside has the fuel door on the driver's rear fender in the front. Replacement (aftermarket) fenders do not come with this in it,.. they come without. The manufacturer states that the fender can be custom cut to fit the door. The factory fender is stamped to recess the door... I'm not seeing how to do this. Is there an aftermarket type fuel neck that mounts to the fender that I can just cut out a hole and install? all help appreciated.