Lift the BOTH roofs into the open position. The torsion bars are now unloaded, under no tension.
Detach the wiring going up the lift arms. You may need to disconnect the A/C cable at the junction box (both TMs I did this on didn’t have rooftop A/C).
Place a table or build a scaffold with a couple step ladders & 2x4s at the ends of the camper. We put a couple old tires on the table/scaffold to act as a cushion.
Remove the pivot bolts on the middle lift arms for both shells. The shell should be resting on the lift arm pocket stop, there really shouldn’t be much tension on the bolts. If you have the old style with the Allen bolt & acorn nut hold the Allen wrench and remove the nut inside. This seems to work better and not strip the Allen bolt.
One person inside the TM pushes the roof up and towards the end of the camper, sidekick guides the shell and carefully sets it on the tires.
Place a 2x4 across the top of the walls of the bottom box and under the bottom of the shell walls to keep it from possibly coming crashing back down while you’re working.
Now you have a nice open area to work on the bag seals with plenty of clearance from the rear shell and lower box.
I’ve attached a diagram showing how to support the roofs, a diagram showing how the shell rests on the lift arm pocket stop (pre-2000 TMs used a rubber pad while newer TMs use a bolt) and not on the pivot pin, and a couple pics when we cracked the project 2720 open to repair the blown out pockets. Notice in the photo the torsion bar isn’t straight up and down when the roof was lifted. We had backed the torsion bar adjusters way down because we weren’t sure what to expect. But the bars are at rest in the upright position, they usually want to stay vertical.
Foam is 1-1/4” x 2-1/2”.
This video isn’t complete and might give you vertigo but it has good info on where to staple and how to fold the vinyl on your new bag seals.
https://youtu.be/BQQRi51umu8
They are walking on the rear roof, but they have a brace they put underneath to hold the shape and support the weight. I wouldn’t do this because I’m a pretty big guy. The folks at the factory are in a lot better shape than I am so they can get away with it.
Let me know if you have other questions, if I don’t know the answer I’ll make something up!