I agree with the above posters, lifting the tires off the ground will do nothing to help save your tires, and it only creates a risk for damaging your camper.
BUT!
If you insist on do it, here's how you should lift your camper (photos below). After getting the tires off the ground, use at least 4 sets of blocks or supports under each side of the frame. One in front of the axle and one behind the axle, and then one about 3/4 to the front and one 3/4 to the back. Rest frame of the camper on the supports. Once lifted, then do the same on the other side.