What Danno said, and this sort of design comes with more drawbacks than simply using a big tent, which is cheaper to begin with:
- have to detach whenever you want to move the vehicle -- same drawback as a truck camper (break down to move it), same reason why trailers have an advantage for "base camp" camping. Set it up once, leave it, drive away for the day, etc...
- gaps between tent + vehicle = insects and rain get in.
- potential for paint damage on vehicle from tent rubbing on it
And the biggest -- why would you want to be able to crawl between your vehicle + tent anyway? Don't see the benefit.
If you have the space in your vehicle, get a big tent and a freestanding canopy for shade/rain. The EZ-Up ones are nice, but there are cheaper knockoffs too.
http://ezup.com/