I had some time yesterday, so I went ahead and bought the expanded PVC and began to mod my car. So far I have done an air dam to cover the extraneous grille on the bottom of the front bumper as well as a belly cover that covers about 2/3 of the bottom of the car. I attached it with screws and zip ties and I'm pretty pleased. Especially because the stuff was unaffected by a rather brutal rainstorm last night.
Haven't done any tests, but I have noticed that it's quieter on the highway. Also, the coolant temperature has gone up from 180f avg to about 200f avg. Sometimes it gets up to 207f. I live in a very VERY flat town, so I'm not too concerned about the engine temp (should I be?). Also, this is when it is 85-90f degrees outside, so I don't expect the car to be hit with much worse. If this is a major problem, I will just move the license plate over and cut a hole for intake (my radiator is in the center).
There is a little bit of duct tape dangling down in the front, I was trying to make a better seal against the body of the car, but the gap was too large and the tape wouldn't stick. Also, there is a black pen line running across the front. I feel kind of stupid, but I was making a rough estimate mark for cutting and I didn't even realize I was drawing on the outside of the car.
It's a pretty smooth surface. I had to cut away near the front wheels to make room for the tires to turn, but I didn't cut enough so it still scrapes. I'll go at it with a saw tomorrow.
It's not exactly seamless. It was very hard to bend the material in three dimensions. I might go back over it with a heat gun and see if I can warp it to a better fit.
I had to cut a hole for the catalytic converter, but the tailpipe itself is still a little too close to the plastic and it causes it to warp slightly. I will be lengthening this hole along the tailpipe in the future. I just have to find something to secure the edges of the hole to the frame.
Although it's not very easy to put these changes on and take them off, I plan on doing an A-B-A test as soon as my new scan-gauge is properly calibrated.