Since there isn't a thread for this yet...I started my 4 channel amplifier install today.
So far I have only run my power cable, and plan to finish my install by the end of the week. Not a lot done, but took my time to make the install clean and figure out how parts came apart. Like the previous generation the power cable can be run through the driver's side fender well which is what I chose to do since I plan to locate my amp under the driver's seat. I used a 4 awg cable which I ran through the extra space in the driver's side floor cable way and ran the cable under the carpet to make it under the seat. I will use a distribution block to transfer power to the amp and eventually if I choose to add one a trunk subwoofer. As far as mounting the amp, I am going to use industrial strength Velcro. For those worried about using Velcro, this is the same stuff we use on our boats to secure stuff for sea that held large objects even in the roughest 15'+ seas with 20+ degree pitching and rolling. Simply put it's not going anywhere in a car.
Tips for getting the inner plastic fender out, there are 3 screw type clips near the bottom rear and another under the side sill spoiler. You will need to remove at least 2 of the other clips to get enough clearance to the gasket.
Definitely recommend using some type of lubricant on the cable to get through the grommet, I opted to used soap.
Update:
Ended up upgrading my original carry over amp finally to a JL Audio XD700/5v2. Fitment under the seat is a lot better, in fact this series of amps are pretty much the ideal size for under the seat even with cables at just over 7" wide. My previous amp didn't sit exactly under the seat and sat on top of the air ducts at 9" wide, but it did fit.
For a general rule of thumb for those looking to add an amp under the seat, anything under 7.5" wide should fit, 7.5"-8.5" will fit if the connections are on the sides. Anything over 8.5" expect to have to not have a flat fitment unless you get creative. Length and height really weren't a problem, a 18" long amp should fit. I didn't do high measurements under the seat rails, but you should have up to 4".
For those interested in removing the driver's side power adjustable seat in a Limited, it's the same as the the regular seats. I ended up removing the seat this time to dress the cables better as my anal-retentiveness with electronics got the better of me. It was fairly simple, remove the two rear bolt covers, undo 4 bolts, and lean seat back being careful not to put any tension on wires.