Hi Jesse
are you ordering a kit or are you sewing the carpet yourself? There are only four pieces that are padded on my kit which i purchased from GAHH The mats in front of the seats, and the two pieces directly under the seats. The rest has no backing There are some diffferences to what was in my car originally though with this kit, but unless someone is an absolute stickler for an identical look nobody would know the difference. The remainder of the carpet is glued in place directly to the underlying metal. Be careful with padding. If it's too thick, it will look funny and you will not be able to trim the car out properly. There are threads on Dynamat and other similar products, but they don't provide cushioning really. They are great for sound and heat isolation. Remember that at the door aluminum threshold the carpet needs to fit into the groove of the aluminum trim. Do a test fit of the piece first to see how it needs to look. The metal trim piece will cause a very small stepoff under the carpet which is palpable if one pushes hard. If you want, glue Dynamat right to that edge, then you won't feel a stepoff. Also, (just a tip from me) if you don't glue the carpet itself all the way to that piece of trim and if you leave a small strip next to the trim without glue, you will be able to tuck in and, more importantly, pull back the carpet and thus remove the trim if you find it necessary to refinish or replace the trim (unless you buy new stuff, in which case it will most likely outlast the carpet cosmetically)
I am myself wondering if anyone has found a nice way to pad under the two pieces over the drive shaft tunnel. Those two pieces don't fit too well in my opinion, even in the original carpet in my car