Seat Reinforcement Brackets = $0
XJ owners have known that the seat base metal tears where it bolts to the seat track. After talking to a friend who has a WJ, he described a similar issue with WJ's. I'm assuming ZJ's have the same problem being as you can bolt WJ & ZJ seats to XJ seat bases.
I found this online, but didn't feel it was substantial enough.
From there I decided to make my own kit out of 1/8" steel that I had kicking around. This can be bought at big box home improvement stores fairly cheap. I think I paid $20 for two 3"x36" sections of 1/8".
Typically, the seat bolts to the tracks with 4 bolts. But there is an additional bolt per side in the seat that is not used. Basically I made 6 plates that were drilled to match the 3 bolt holes per side. One plate is sandwiched between the seat track and the seat base on both sides, and a 3rd plate runs above the seat base on the outboard side, being as that's where the metal typically rips.
Template made out of cardboard.
Here they are almost cut out and test drilled. They may not be pretty, but after a wire brushing, and some paint, they should work out pretty good.