The Lance 815 I know of for sure and I've seen a couple of others that did the same to handle the difference between the truck bed lengths. On the 815 and it's the only model I know of which they did this with is have pods that bolt onto the rear of the camper when you put it on a short bed truck. The pods gave a little extra storage but more importantly had built in lights. Because the camper was very light at only 1,600#, having the COG a few inches outside of the recommended truck's COG was not a problem. Moving the camper 18" on my LB truck will only shift about 300# from the front axle to the rear axle.
So on a long bed truck, you had the option of removing the pods and letting the camper slide all the way forward in the bed which meant the camper stopped at the rear bumper. Or, you could put a spacer in front of the camper so it sat back 18" allowing you to leave the pods on.
On a short bed truck, you left the pods on which provided tail lights at the rear of the camper and the camper stuck out 18".
Any other short bed camper can go on a long bed truck because the differences in the bed lengths are all in front of the axle. So the difference in the relationship between COG and rear axle is zero between the truck beds. You do need to build a spacer (usually 18") so the camper has something to push against to prevent contact with the tail lights.
