Nathan,
It is hard to see but the bracket I made curves up and to the inside of where the welds are. The edges around that corner are steel and not the aluminum so you can ground there. If you look on the inside panel you will see the seams and welds that I am refering to. LR has some of their factory grounds wired to the same location. An extra ground that runs from the back of the anntena plate also runs down below to where the bumper mounts.
Go to Pepboys and tell them you need a engine grounding strap for a 1989 jeep wrangler. this is a 16" breaded flat grounding strap that will fit perfect. It is designed to ground the engine block to the frame and it is also only $5.
With the tunable Wilson 5' FGT I ran the recommended 18' of shielded coaxial cable and then did test on the line and antena. it is supossed to be 50 ohm. It was a bit short, so I grounded the extra (optional) wire at the base of the FGT to the antena mounting plate and got very close to my 50 ohm. I just need to fine tune the SWR.
On the interstate the other day I was comunicating for a 5 mile radius. the week-before was 3 miles. Really good for it not to be fine tuned yet, plus I still have that small Cobra 19 (POS). plans are to put in a Galaxy 949 and have it flush mounted where the ashtry is.
If you are going to be at the BBQ in a few weeks I'll show you the details. If not yet me know, I'll be near your office next week.