Doug33 wrote:
Do you need to notify Walmart if you are parking overnight, or just pull in and go to sleep?  Do you park as far from the store as possible? What do you do if it is really hot weather?  Parking lots are notoriously hot in the summer, although theoretically things cool down at night.  Can you run a generator?
1. There are Walmarts that do not allow over-nights...
see http://www.walmartatlas.com/no-park-walmarts/
2. For the ones that do, it is preferred that you do not look like camping, although I have seen chairs! 
3. I was told by the manager that they also prefer you go to the back of the lot to prevent traffic problems, but we were told to have a good night! Then we spent $130.