It's the one that covers the transmission/transfer case (thanks deby, added the transfer case part) , it's a must have part. I don't know if the trooper you have has the same one, but if you do a search there's a part number for it. Also, it's a perfect fit, no modifications needed, the frame has threaded holes for it, don't know why they didn't add it to begin with. Just make sure you buy the extra bolts, part numbers again will be in the search. Other than that I just had 265/75/16's, with a spare on the factory roof rack. The picture you see next to my name was a picture from the Moab V trip.

OH, and a good cb radio...