Tim isnt wrong, but its not a bad thing to do either. Let me put it this way, If I lived in texas.. I would still get mine undercoated. I dont live in that area but I highly recommend that you keep your brush guard or get one if you dont have it. Alot of people take them off and it hurts you in the long run when you need an impact wrench to work on your engine
Oven cleaner? Just spray it on everything and let it sit for a couple minutes and then pressure wash off?
I don't really understand what this has to do with keeping the underside of a Jeep clean? A brush guard will protect his headlights and grill from trees but otherwise?????
Should it be assumed that you are talking about that piece of plastic/rubber that Jeep put between the engine and the steering components?
If you go to most large truck stops, they will have a company that cleans big rigs. They use not just high power water, but steam with degreaser. If you want, they can even take the undercoating off.