It doesn't have to be all that high... just enough to get the tires off. I used 2 unijack bottle jacks
, 4 jack stands, and a number of 4x6 wooden blocks. You'll notice the unijack has a "saddle" at the top vs just a standard flat round... I don't really trust the flat rounds to stay on the frame.
I jacked up one side of my rig using the unijacks.. alternating a couple of pumps at a time, used stands and blocks (one directly under the frame to help spread the weight load across a longer point of contact, then the jack stand, and additional blocks under the stand to get the right height without having to extend the jack stands too high) to support that side about 3 feet or so in front and behind the wheels, then did the other side the same way. To further stabilize it I blocked under the scissor stabilizers and extended those, and blocked under the front trailer jack. So basically, each side of my rig had 4 points of contact/support.
I should note.. the entry door side of the frame had a wiring harness running along the bottom of the frame forward of the tire well that I had to move to the side of the frame during the flip... and needless to say.. this needs to be done on a hard flat surface.