Well,
Everyone's got their opinion on whether or not to climb under a rig that's only being supported by it's own leveling jacks. I've done it for years. Yep, I know, you're trusting all the hydraulics of the jack system. It's a personal preference thing for me. I do use two, 4" x 14" x 14" blocks under each jack though. I place the blocks under jack pads, which are only about an inch away, then I release the air in the bags. The rig will drop automatically down on to the blocks.
From that point on, there's enough extension in the jacks to raise all six tires off the ground. I can then do what whatever work's needed, brake inspections, wheel polishing, oil changing, trans oil changing (although since the introduction of Transynd, no need for another 95K miles, yahoo), and more. Someday I'll get some large Jack stands for use under there. But, until then, it's as stable as a rock and, level as possible.
Scott
Scott and Karla SDFD RETIRED2004 Itasca Horizon, 36GD Slate Blue 330 CAT
2011 GMC Sierra 1500 Ext Cab 4x4 Toad
2008 Caliente Red LVL II GL 1800 Goldwing KI60ND