Just curious Rick, have you ever done this? How? I'd be interested in knowing. Thanks.
First, let me say thanks to Bob&Patty for the acknowledgment. Bob, you got it exactly right, and I'm happy to have helped a little.
Second, no I have not found a confident way to insulate the slide end-walls, roof, or floors. I haven't had a pressing need being in North Carolina and Florida for the last 4 years. I have often wondered about full-timing in the winter up North, though.
The end-walls, I am told, have little or no insulation in them. I have wondered if you could use expanding foam (Great-Stuff) without causing structural damage, warping of the fiberglass skin, etc. The only other option would be to remove the exterior skin and install some insulation.
I'm not familiar with the slide roof construction, so haven't been able to put much thought there. We have slide-toppers which have to reduce the summertime sun load, but do nothing for heat-loss. The slide floor is basically nothing but single-ply particle board, so there is no permanent mod you could do there to insulate. The only thing I can picture for adding insulation for the floors and roof would be to again, use 2" insulation board installed temporarily on the exterior surfaces. On the roof you might be able to secure them from the top side with a couple small tension rods between the RV wall and the outer sealing flange on the slide. Under the floors, again I haven't put enough thought into it, but I'm sure something could be done.
The foam panels could be cut to size, painted on edges and exposed faces for weatherproofing and aesthetics, and numbered for proper location. With the right planning and a little luck, they probably would all fit in the basement for transport and re-assembly.
I'm not sure if it would be worthwhile, but if I was going to be up north through a winter, I'd probably find a way as I don't like being cold or buying propane.
Good luck, and keep us all informed.
PS - Our rig does not have dual pane windows. I have used shrink film on the larger windows that don't get opened. It helps quite a bit, but is a pain to put on. I've used the double-sticky tape on the aluminum frames generally with good luck.