I have 2 six ton jacks I use on my 24,000 pounder That is half the weight.
HOWEVER that said. I can crawl under my rig when it's all the way down (Good ground clearance) and it's getting easer to do as I loose tonnage (Personally) as well.. Down about 1" or 20 pounds fron what I was.
But I use the six ton's in the rear and 4 in the front (2 ton each) and never fully unload the springs or lift the wheels off the ground. Have not had an issue doing that.
My RV" hydraulics are ... Non functional at the moment