Being a perfectionist and an engineer, I actually get a tape measure out and measure all four corners to ensure I'm within 1/2" of alignment all around. What I have found is that it is easy to get the front OR the back evenly aligned side to side but getting BOTH front AND back aligned is very difficult because turning the truck affects alignment in both places.
Being in the manufacturing business, I it is on my todo list to build alignment guides that utilize the bed bolts in the truck with two flat plates of 12g stainless steel that fits under the camper side to side (one front and one back) and angled vertical guides that attach to the flat plate on either side with padding so when the camper is lowered, it self guides into place (assuming you have it reasonably close so as not to put too much pressure on the jacks). Many people have done this same thing with 2x4s, so it's not a unique idea but having something that bolts into the bed of the truck (and is removable when not needed) I think is what would separate this idea from a home built system out of wood.
In addition to the above idea, I have in mind to build casters that attach to the bottom of my jacks. What I would do differntly however is that I would not have castors that pivot, just straight casters and they would be mounted for side to side movement (truck bed is North/South but casters on camper allow movement East/West). With the casters aligned East/West (and non-pivoting) it is a matter of backing the truck close enough and then to roll the camper side to side so that the receiving metal guides in the bed will do the rest.
I think the system would work well and it is on the todo list to design and build but my time is pressed in other locations right now.
