Lew is pretty much right on there. Having a reproducible frame of reference is useful though. It really isn't that hard to build layers of 2x8 scrap lumber so that you can level side to side. With severe slope it might be difficult to get the tongue jack on anything solid. Be sure to put blocks against the wheels to keep things from rolling!
Level is overrated.
This is an art museum at the University of Minnesota. You might come up with a similar creation if you step outside of the Flatland world ...
