Yes, there are three pieces that you need to order through RockAuto.
I just took the part numbers that I have saved and entered them in again. It came out to $392.36 shipped to my house, so the price increased by a few dollars.
That includes the mass backing.
I got mine without the mass backing. Just arrived this past week. I have not opened it yet. When I ordered mine the complete set with mass backing was more like $500 and it came up under the one without the mass backing. Weird. Had I known it was only another $40 or less. I might have gone in that direction. But I'm putting down a layer of Second skin sound deadener and foil backed auto insulation on top of that. Fortunately the ACC comes with extra carpet around the edges. So it can be cut to fit. I'd imagine all the stuff I'm putting under it will use up most if not all of the carpet. So I doubt if the mass backing would have fit too.
I'm going with the sound deadener and sound/heat/cold insulation to better buffer the inside of my Jeep from the outside and the reverberations on the metal pan. I think the mass backing will help with buffering outside noise. But it won't do anything for sounds reverberating from the metal pan. But then you have, like you mention, the ease of removing it to get rid of water or mud. I don't take mine out mudding or anyplace where water is going to pile up inside. So I don't have those same needs.
This might not look like the premier site to buy auto insulation. But it is.
http://www.carinsulation.com/ It's the best stuff you can buy for a heat barrier. And it also is a sound barrier as well. USed widely in the hot rod industry. It used to be called auto insulation by Lubocrud. But has since been bought out by the site above. Look at the specs. It's pretty amazing stuff. It takes a very small amount to do a Jeep pan. Be sure to get the aluminum tape with it. And use 3m Adhesive to get it to lay down. The nice thing about this stuff is, although it's thick, it's very lightweight. You won't be adding any appreciable weight like with the sound deadener. So it's great to use in combination with sound deadener or even by itself. If all you need is a heat barrier.
I don't know the specs on Home Depot aluminum backed insulation. You might be able to do a similar thing with it and aluminum tape.
But here's the specs for the stuff from carinsulation.com:
Features & Specifications:
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