The best approach for those type stabilizers is to have them make contact with the frame, or something solid that is attached to the frame, which may require you to get up under the rig a bit. Open them until snug, but not beyond. Do not attempt to do any leveling - even a little - with them. Do not put them under the slides. As spyder152 indicated, try to get them on the 4 corners. PM me if you want more detail. A long time ago in a land far away I had a pop-up with scissor jacks... As for having them bolted on, I couldn't say without more detail.
DAT in TX
2018 Vista LX 27N
2015 Jeep Rubicon and ATC Open Car Hauler