I noticed that my rear springs were starting to sag from being over compressed. I could actually see marks on the coils where one coil was hitting another. I decided to make some bumptops. I looked at the hockey puck idea and modified it. I have about 3.5 inches of lift in the rear of the KJ (measured before the sagging probably about 3 inches now). I looked around and picked up two of these from my local Bass Pro for about $8 total. I used plain black silicone as an adhesive allthough you could as easily use a 1/2x4 bolt with washers and drill through the spring perch. I used the adhesive route becasue I didn't have a drill that would fit between the spring perch and the upper bumpstop.
If you don't need the full 3 inches, it is easy to cut this rubber down to the length needed and just change the bolt size used. These don't seem to compress very much and are just a little smaller in diameter than the center of a rear spring spacer. It seems to work well so far. If I have any problems out of them I'll post an update.