[JRTJH]

I have four 6x6x12 cedar blocks that I stack on top of an "adequate number" of lynx levelers. Sometimes, depending on the slope of the campsite, my rear jacks have been 36"+ off the ground and I've had a foot of lynx levelers, a 6x6 cedar block and still had to extend the scissors jacks to "near full extension" to get them to rest on the blocks.

Typically though, a couple of lynx, a single 6x6 block and the scissors jacks will extend about half way and stabilize the trailer. I wouldn't want to install 30" scissors jacks, when closed, they would be "right at the edge of the trailer and that's right where my grill propane connection is located.