You guys have great logic, but I can still tell you in spite of the logic, I have no problem supporting my camper with a single front jack and two rear jacks.
My camper is a Northstar Igloo with an extended cab to accommodate a N-S orientation for a full sized Queen mattress. If I jack it up and look at it from the side, it appears in danger of tipping over frontwards. That is not at all the case. In fact it can be used supported by the jacks and that use can include at least a couple of heavy people in the overhang.
The camper COG is just not as far forward as it appears. Few of us have scales but there are a couple of ways to determine this. First at least for my Northstar the manufacturer has specified the COG. It is only a little bit forward of the center of the floor area. Second you can weigh your truck and then your truck with the camper. My camper is about 4000# fully loaded. All but about 100# sits on the rear axle of the truck. The COG is only inches in front of the rear axle and again that is close to the center of the floor.
There is another factor that helps. Proper use of jacks means keeping the nose of the camper pointed upwards by a couple of inches or so. That shifts the COG further to the back. In fact I would guess it takes only a few inches of lift to shift the COG so that more than half the weight falls on the rear jacks. It is not necessary to shift more than half the weight to the rear. You can end up with say 55% of the weight on the front jacks and even amounts of the remaining weight on each of the rear jacks. Then lower one of the rear jacks. That will again shift the COG and will tilt the camper to the point where the diagonal front jack will be off the ground.
All I can say further, is try this for yourself. It will work, or at least it does with my Northstar.
