Camper / Bed Alignment Products - Do they exist?

Yes, the HJ front tie down bracket has bumpers to keep the camper from shifting side to side. Installed properly there is 1/8" gap between each bumper and the camper. Personally that's enough of an alignment as I think letting the back float a little is a good thing. The tie downs will keep it right.
But if it bothers you that much you can do something similar for the back, just fabricate a couple wood spacers for each side and use some rubber bumpers that stick straight up.