You may want to tell how long the period of storage will be. I'm not sure "most" use their jacks in storage but many (some) do. I have never used mine that way and my ten year old tires did not show any ill effects when I replaced them earlier this year. As long as you have the proper tire mounted for weight etc; then MO is you are fine. I covered my tires which seems to be a good idea.
5% incline---not too much I believe. Just block the rig so it cannot roll, of course. If you are worried that the incline may leave an engine bearing or seal exposed then just reverse the coach periodically if possible. Perhaps the incline could be lessoned by driving the rear wheels up onto leveling blocks (is that what you mean?) They are used by people who do not have levelers when they are camping so you may need some anyway. Some two by tens can be used to make these blocks, make sure you have them under both duals at each end of the axel. If the tires are on blocks you probably do not need plastic unless that is used to preserve wood blocks.
Other things to think about are your batteries (can you keep them charged), your water system (is it winterized) and your grey and black tanks (are they flushed and drained)?
I do all my own stunts
03 Dolphin LX 6355, Workhorse W22, 8.1 vortec, 04 CR-V, Blue Ox, Brake Pro----Norm, Barb and
Doc(He's a PhD)