the stock cherokee's with the nut strips (having a rear tow hook, stock skid plate, or reciever package) would be much easier to do this on. Otherwise you have to fish nuts through the frame.
To install it, if you have a reciever or tow hook:
the sikd goed below the reciever, so the when its done, it should be frame rail, reciever mount, gas tank skid mount in order from top to bottom.
remove tow hook
use jack to lift skid up to gas tank.
line up holes
use provided bolts and bolt into factory nutcerts
torque them to some spec... IIRC should be 63 foot pounds
then go hit stuff
Without factory nutcerts - 2 options:
1 - take off rear bumper and fish bolts thru holes and hope you put the right one in the right spot, then have fun and follow above instructions
2 - go to dealer and spend $20 on nutcerts, take off rear bumper, slip nutcerts in, then follow above instructions...
hope this is helpful