We use Walmarts a few times a year for overnight stays, usually under 8 hours. We'll be doing in a few days actually. We generally put the bedroom slide out. We don't have to, but it's just more comfortable. If we need the A/C or the Heat, we run the generator and the A/c or heat.
I hear people say it is generally frowned upon to put slides out or use the generator, but I don't think most people realize that. It's rare to stop at a Walmart, even ones that are miles off the interstate, an not find at least 1 other camper there with slides out. What I think should be frowned upon are the folks that put the awning out and pull out the table and chairs like they are at a campground. We did that once at the Target in Owings Mills, MD, but that was because our Tow Vehicle was at the Chevy dealer next door and we had nothing to do, but wait. We were there a few hours and left. We did ask the manager and we did make some purchases there.
To each their own. Walmart welcomes RVers (even says so on their web site) and until they tell us not to put our slides out or use our generators, I will continue to enjoy their hospitality.
-Michael