When I lifted my shell off of the frame:
1. I think it was only held on by the mastic tape
2. All of the fasteners, from inside the shell to the frame, were corroded away
3. I jacked up at all four corners simultaneously.
4. Pried it loose a bit at a time
5. Got it high enough to put some 4X4 from side to side
6. Blocked those up to allow for clearance between the frame and the shell
7. Jacked the axle
up a bit
8. Took the tires
off of the axle
9. Placed some scrap plywood under the hubs
10. Dragged the frame out from under the shell.
It took me some time since I was outside in a semi-confined space. (only a foot or two clearance on each side) Also was working on the dirt, mostly during the rain and snow.
It is not a really big or specially technical task. Just take it in small steps. And, be careful.