Sounds like you are in for a great time. Are you planning on leaving the car parked the whole time? If so, then maybe it would be worth getting an air mattress for the back of the HHR that would be off the ground some and more comfortable.
We got an Eddie Bauer screen room from Target last summer that we used for the trip and it was a great find, fairly easy to set up (although my 8 year old helped, so not sure if it can be done with one person). We got the Eddie Bauer because it was fairly well built and had many different places where it was tied down to the ground - something that might be really important during the summer thunderstorms that pop up. We never had a problem with it blowing over, it had about 16 stakes to hold it down, including about 6 tie down ropes from the top.
I would think that you would want either a good dorm fridge or maybe a 12volt cooler for this kind of trip. The more I think about it, you will probably want to keep the car separate from the tent, because you are likely to need to get out frequently for less expensive food at Wal-Mart or Publix.
I hope you have a great time and post lots of photos. Also, if you need help setting the screen room up, let us know. I could probably convince the family that we need to go back down to help you out. You know, it's the neighborly kind of thing to do and I'm looking for any excuse to go back.
