Noxman, I'm unsure on the thickness; it's probably about 3mm I'd guess. Thinner would be better, I think, because it would flex easier.
Phil - I have some reflective tape I've been meaning to add. Eventually I want to put some taillights out there. Luckily most seem so distracted by it in parking lots so far that they're more likely to run into something else!
One thing I noticed the other day - it is bad in the rain; water from (I guess) under the car sprays up on the underside and makes it opaque to all but headlights. This will hopefully be improved when I clean up the bottom and the sides of the car though.