I just did some "skid plate work."
I replaced my very bashed up transfer case crossmember with a new one from Poison Spyder. It is very beefy and certainly much stronger than the factory unit. It was a fairly easy bolt-on operation, and my only gripe is that the unit was only available unpainted. Prepping and painting the piece was not fun and took a while. And since that support sits literally an inch away from the exhaust, I was little worried about heat on the newly painted crossmember. I also had to drill two holes to accomodate the transmission wiring harness clips.
(Just as an aside...it amazes me how much stuff Jeep has to protect with "heat shielding" underneath a Wrangler...scary!)
At the same time, I replaced my badly dented gas tank skid plate with a new factory unit. I thought this would be easier than installing an aftermarket unit, but anything involving the gas tank is a pain as the skid plate is what holds it in place. Swapping out the gas tank skid plate can be done without removing the tank completely - I used straps - but make sure the tank is as empty as possible.
As an afterthought, I also installed a RockHard secondary gas tank skid plate. This was a simple installation, the hardest part of which was drilling two holes in the factory skid. The RockHard kit was very well made, and can definitely take some abuse. All the needed hardware was shipped with the kit, including special collars for the crossmember bolts to prevent bolt head damage. Nice.
In retrospect, though, I wish I would have just gone with an upgraded after-market skid plate from the start.
And finally, I repainted my transfer case skid, which held up surprisingly well compared to everything else. There were a couple of big gouges from the rocks, but nothing substantial.
Next up will be a skid plate for the EVAP cannister as that bad boy is only one rock or log away from total destruction. I can't believe that Jeep made no effort to protect it.
One last thought: I'd be careful with bigger area skid plates for the transmission and transfer case. There is a lot of heat generated on the undercarriage as it is, and if that heat cannot dissipate, bad things are sure to happen. As I mentioned above, the amount of heat shielding on the undercarriage, including many of the cables, is a bit disturbing.
I hope this information is helpful!