I am right in the middle of the same project but I put down a layer of sound proofing in the back and am using the thicker regular German Velore carpet (not the RS).
Buy LOTS of glue. I am about half way done and through three cans of the 3M spray on stuff. You need to coat both sides to be bonded, let it dry for a few minutes then lay the carpet.
Make sure you find any holes where bolts or screws need to go before the glue dries (like the rear seat belt bolts). If you are putting the rear seat backs back on, don't forget to cut out holes for the hing pins on the sides.
Those are the tricks to the trade I have learned thus far.
Good luck
Chris McFaul
73 911 E
Ps this is what you feel like after breathing in the glue fumes for a few minutes
