Dennis,
I believe what the Chuckster said 100%. However, my comfort zone is having all 4 wheels and the 4 leveling jacks on the ground.
Here's what I do if I get to a site that isn't level side to side or front to back or (usually) both:
I use the Camco Tri Leveler under the low side wheels to level side to side. Then use the front landing gear (tongue jack for your buddy) to level front to back. This gets me pretty close. Then I engage the leveling system (auto level). That fine tunes the level for the entire rig. Whole unhook and level process is less than 15 minutes.
I also use the stacking blocks under the landing gear and leveling jacks. Again, raising the low sides as needed.