I had an inverter in my previous car ('92 Stealth ES) and found it invaluable for keeping cell phones, laptops and other devices charged. Sometimes it is hard to find 12V adaptors for things.

In my '09 MCS, I I built a little harness to go in-line with the rear power outlet and ran two 12GA wires from it under the boot side-panel to a Weigand 125W inverter. I modified the foam block under the boot "floorboard" to accomodate the inverter. I put the inverter down against the metal in order to allow it to cool better. I then ran a heavy-gauge 6' extension cord from the inverter under the "carpet" and under the rear set. I now have a 3-outlet "block" that hangs out just in front of the rear seat. For a test, I ran a 60W "trouble light" during a 3 hour drive and nothing got more than warm.

Not too elegant, but it works!

 

That sounds like a neat setup. I keep an 800W inverter and a short extension cord in the trunk, and just hook it up to the battery with alligator clips on the rare occasions when I need it. If I used it more than once every few months, I'd probably hardwire it, but I'm also usually powering stuff outside the car rather than inside the car, so my setup would still basically just be an extension cord in the trunk.