I found this on a friends site....should aply to your Jeep too.
PART THREE: IGNITION WATERPROOFING AND IMPROVEMENTS
This is the only part where you actually have to do anything requiring much effort, besides crawling under the truck to install the vent hoses.
Plug wires:make sure they're in good shape. I put a little bead of RTV inside the boots on both ends, plus a little bit around the joint where the boot ends and wire begins (I guess I'm kinda a belt-and-suspenders man when it comes to this).
Distributor: I have read of some pretty exotic treatments here regarding closed-cell foam and duct tape, but I have found it to not be necessary. The distributor on the 4.2L is rather low, below the spark plugs, but my system works quite well. I have never had any problem with water in the distributor, which is quite regularly totally and deeply under water. What I did was pull the cap off, and run a bead of silicone around the bottom of the cap, where it meets the distributor body. That's it. Accel and perhaps other aftermarket caps have an o-ring around the bottom of the cap, so if you have one of these, you probably don't even have to bother.
This leads into the promised improvement.... if you have a '77 and up 4.2L, switch to the Ford 8MM two-piece distributor cap. This will help with the cross-fire problem inherent to these engines. Run a little RTV around the bottom of the base cap, then also at the top, where the top piece goes on. There is a double lip on the top cap to fit over the base part, so this may not be necessary, but I do it anyway. Another advantage to the two piece caps is the flapper valve vent on them. I suppose you could modify that just like the drive-train, but I haven't bothered.
Rob 8)