Our 2-person camp set up is looking to be like this:

That's a NorthPole Party Shade tent (thanks to eplayans for the recommendation on these)... a rented RAV 4 (or similar, depending on what Hertz has for me)... a Sierra Sirrus 3 tent... and I'm thinking of rigging a tarp to the roof rack to create a shady/cover for the tent.
My questions are:
Would you suggest a ground cover for under the North Pole shade structure? If so, what do you suggest? Not carpet, not astro-turf... I'm thinking some sort of tarp, but not sure what kind would be best and how to secure it.
Also... do you think the additional tarp rig-up from the vehicle is overkill? Maybe we should just put our tent under the NorthPole structure?
Additional questions I have are: where to keep the water -- in the vehicle? (hot sun + plastic = death???) And where to keep the cooler -- I was thinking sandwiched between the tent and the vehicle under the rigged shade structure.
Any other thoughts appreciated.
Thanks!