And...you do NOT
want to permanently cover that access port. As sure as you do, something will go wonky with the sender and dropping the tank will be your only option.
Mine did not originally have access but I installed a hatch that is now accessible from the storage area under sofa/sleeper. Since I replaced both the fuel tank and the fill neck, adding access to the sender just made sense.
It is the rectangular area just inside where the fill neck is located.