I got one just the other day and they seem pretty wicked.
I havent tried it out mounted to the outside of the truck yet but it does mount by a dirty great motorsport approved suction cup...rated to 120mph so i read.

And here is a wee vid of some fella in a Toymota Tacoma getting stuck with a motorsport hero camera recording.
some guys getting stuck
Will try it out next time i go out and let you know how it works out.