My 90 GeorgieBoy Cruise Master was on the JohnDeere/Oshkosh chassis.( Ford 460) I lowered the 90gal. gas tank by using long sections of all-thread to replace the bolts, with washers and double nuts to support the tank. Used floor jack and 3/4 ply under tank.
I was able to get the tank below the frame and then tip the tank enough to replace the wires that the squirrels had eaten at the top of the tank.
Have seen several discussions on cutting a hole from above to get to the tank, I've not heard of any success. Most end up with a frame or obstruction in the wrong place.
Good luck...
Hooligan U.S. Coast Guard Ret.
2016 THOR Siesta Sprinter 24ST Diesel
2008 SUZUKI Grand Vitara TOAD
1 Pug "Lily", 1 Newfoundland, "George"
1972 MotoGuzzi Eldorado