Originally Posted by Stu & Filo. T
Looks to me it's to access the fuel level sensor only, so if it was mine I would cover it & if you ever have a problem with it just drop the tank, it really isn't that hard & I've dropped quite a few fuel tanks & even did the one on my bus with about 60 gal of fuel in it, best way is use a transmission jack with a piece of 3/4 plywood on the jack cut down to what ever size you need to keep it stable.
Oh boy.... Have you dropped a school bus tank yet? I have. It's not fun. The tank is usually protected by a cage made out of 3/16" walled 2"x3" steel tube. The cage alone must way close to 200lbs. I'd keep that hatch somewhat accessible. Even if it's inside a cabinet that makes it difficult to reach it'll still be a smaller job than dropping the tank if you need to muck around with the sender.
In regards to the fuel gauge not working, mine was in the same boat. It would always read somewhere around 1/4 tank. The problem ended up being that the wires were corroded. The sender worked fine. I ran new wire, cleaned the contacts on the sender and it's been reliably reporting the tank level since!
EDIT: Oh, and I should add that all that work was easily accomplished by climbing under the bus to run the wire then making the connections through that access hatch. A year after that fix I did end up dropping the tank to paint it, relocate it and mount it with lighter brackets. I made a new access hatch to reach the sender in it's new location.