Fairly certain you will have to lower the tank. BUT:Rumor ??::
Some MH may have an access panel in the floor above the tank, or some owners have cut one. My 90 Cruise Master did not..
Long discussion here about the Ford Chassis. Ford 460 Fuel Issue
I have lowered a tank in a 90 GBM - John Deere chassis to replace wiring for the sender. (*%#@* squirrels) but I've not worked on a Ford chassis.
BTW in the link above they talk about the tank "banging"- this is normal as the large tank expands and contracts.
Hope this helps and welcome to IRV-2