I have found the most scenic places are sometimes near the edge of a drop off and sometimes are not nearly level. Same goes for those "Leftover sites" that are the only ones left at 8 pm on a Friday night, after I got off work.
Simple answer. Your tires are only rated at about 3,000 pounds each, while the rear axle is over 11,000 pounds, so you MUST support each tire, not just two of them.
To this end, I used 2X10" lumber, and cut the top level 9" long, with each level below that 4.5" longer (so 13.5, 18" and 22.5" if you need that many levels) I made mine 4 levels thick, and 4 ramps.
Sometimes I only needed to support one side in the back and the same side in the front. Sometimes I would need to raise the front tires on all 4 levels, it is still low enough that I might need to put another ramp or 4X6" block (about a foot long) under the jack foot.
Once I was in such a off-level position, that I flipped one ramp upside down, then put the other on top of it, then drove onto both ramps, bringing the tires up about 8 - 10", then put two blocks under the front jack. Everything was good, however my steps mid-way down the center of the RV was way off the ground. This was a extreme condition, where I was on the worst part of a circle around a campfire out in the desert. More to prove to my buddies "I can level up anywhere" than anything else, and also to show how quickly I can set up my motorhome - compared to their Weekend Warrior fifth wheel.
Fred.