I've been sitting on similar research and a bunch of Second Skin Audio sound deadening materials for a couple years. I don't think Noico was around back then. Or at least if I had noticed it I would probably have gone in that direction. But I hit a yearly sale at Second Skin (which is just as good if not better - it does have black backing that doesn't come off on your hands) and it ended up costing me very little compared to other similarly rated products. They also sell a "B" quality that is just roll ends. That works exactly the same it's just smaller pieces which would work fine for a Jeep.
I used to hang out on the Samba. The VW forum. And there is alot of talk and research on this for busses. As they are typically living quarters as well as a ride. All agree that Dynamat is way over priced. And that you need a sound deadener layer and a mat sound/heat layer. For both holding the heat in in the winter and keeping the cool in in the summer.
So I also bought a heat shield/sound deadening layer for going between the sound deadener and the carpet. Or on top of the sound deadener with 3M adhesive. It's here
http://www.carinsulation.com/ It used to be called "
EZ Cool Insulation by Lobucrod". (if you want to research it) But now it just goes by "car insulation" on that one site. He got out of the business and someone else took over. It looks like a do nothing website. But it's raved about on all the hot rod forums (especially on Jalopy Journal IIRC). As many sound deadening and heat strategies add a second layer of some form of mat to further deaden sound and/or heat.
It's about $80 for an entire jeep. Specs are as follows:
Reduces unwanted sound & most vibrations
Effectively blocks 97% of radiant heat transfer
Keeps your interior cooler in the Summer & warmer in the Winter
Extremely light-weight, flexible, & crush resistant
Creates a mold & mildew resistant vapor barrier
Non-toxic & fragrance free (Will not smell)
Very easy to cut, handle, & install
Nominal Thickness: 1/4"
Temperature Rating: 200 Degrees nominal
Core Material: Polyethylene closed cell foam core
Minimum Installed R-Value: 1+ (Varies depending on installation & vehicle)
Outer Material: 99.4% pure polished aluminum reinforced facing
Double Sided: Yes (Aluminum on both sides)
Mildew & Mold Resistant: Yes
Weight: 0.04lbs per Sq. Ft.
Water Resistant: Yes
Adhesive backing: No
Non-toxic: Yes
"Creates a mold & mildew resistant vapor barrier". This is important if your doing your doors. (and everywhere else in the car for that matter) Once you get your door panel off you'll likely encounter a vapor barrier to keep moisture out of behind your doors. If you can salvage what's there keep it. Or use another type of poly. My strategy was to use this car insulation over the sound deadener on the inside of the doors themselves and then over the window opening in the bottom part of the door as a vapor barrier. Cut to shape from hopefully the original - it would work really well. Both to keep moisture out of your doors but also to provide another layer of sound and heat barrier.
But the real reason I like this stuff is it's really light weight (not to mention it's great stats above). Like a huge roll of 80sqft can be held up with a couple fingers. You cut it to fit and hold it down with 3m Adhesive. Not to mention it provides added padding to your carpet. Think of it as house insulation over your adhered sound deadener. One traps the vibrations/sound and the other more of the sound/heat.
SO if you live in an extremely cold or hot climate it will help alot with heat and cold. Not that we have that much of an issue with that with our great heaters and AC. (Not being sarcastic.) But it will definitely help with heat and cold and sound.
On the topic of water. I wouldn't be worried about sound deadener itself getting wet. It's pretty much impenetrable. But the tiny grooves and edges and pockets left between or under the sound deadener could very easily trap water on the metal surface of your tub. As hosed water would work it's way into the edges and seams you create. I don't think light rain or a small leak would be a problem. But I don't think I would hose out my vehicle after this.
Unless you used a lesser strategy of just applying a few large swaths of sound deadener on each "panel" in the jeep. That weren't touching each other. Then just make sure it's worked down good. And you leave it open to dry overnight. Point being the water won't be able to get under the properly adhered sound deadener. Especially along the edges.
But even adding single sections of this stuff to a given metal panel can result is serious gains in sound deadening. As it stops the vibration as long as a minimum of the panel is covered in the stuff. That's why you see it used so conservatively in modern cars. Even older cars. My bugs had it as thick tar paper with a terribly good adhesion quality. You'd have to use dry ice to get it out. But only over the driveline hump and a couple other places.
But in most cars whatever sound deadener they use it's usually not covering the entire surface of the cabin. Just big patches of it over each panel. Leaving the majority of the metal not covered. In terms of water getting under it. I'd think you'd have a better chance of adhering single sheets to the metal. That water couldn't get under. And with wide empty patches around each section of sound deadener the water would have a place to go and evaporate.
My point is that I think even if you wanted to hose your Jeep out. You could still use this stuff. Sparingly and get great results. But once you put it down I have no idea how to get it out. So keep that in mind.
Once I pull my carpet and put this stuff down. And take pics and do a how to.