should i raise tires off the ground for long storage

For that length of time I would put the rig on RR ties and get the tires off the ground; or at least take the load off. You might also review the suggestions on the Michelin website: https://www.michelinman.com/storingTires.html

nykolas wrote:
for a couple of years at least

That's quite a while. I'd elevate them or maybe spin them around every year so a different part is making contact. Also, how old are the tires? It might be time to consider changing them when you do eventually move.

Aside from the tires, if I were leaving my RV stationary for that long I'd throw it up on the blocks just for my comfort while using it.

I no nothing about fifth wheels in regards to tires. But for my MH Goodyear says to use the levelers to reduce weight on the tires and to inflate them 25% more than normal to reduce flat spotting.

No. Something between the earth and the tires is somewhat beneficial but also not required. Maybe something like plastic or plywood if on dirt.

I agree but protect from sun damage.

You probably don’t need to and most don’t but I do for peace of mind when our trailer is parked longer than 2-3 months.

do not think so but place something under the tires so they are not on the ground and get tire covers