Sounds like you have covered pretty good. If you have a battery kill switch, make sure it's off. Are you keeping the camper plugged in all winter so the on-board battery will charge through the the trailer, or removing it and storing elsewhere. The battery is the only other thing you really need to consider, how you will deal with it over the winter.
And yes, make sure your holding tanks are drained and a bit of Pink Stuff in them to keep the valves lubricated over the winter.
If you are 100% shut down ... no battery, no electricity, no water, no nothing, then it does not matter if you are off level.
I started removing my P-traps under the kitchen and bathroom sink. I can't do that on the shower, so make sure a generous amount of pink is poured down the shower drain. Once P-traps are removed, I know all water is out and no chance of freezing. I had one freeze up and break a few years ago ... never again!