Most China-marts (I mean Wal-marts) allow RVs to stay overnight. RVs being self contained and all. I don't think I would pop the top though- you would attract a lot of attention. Many cities/towns/etc. have ordinances against overnight parking or camping- check with the local police for legalities. That said, I have spent the night in Waffle House parking lots, Wal-Marts, K-mart, truck stops, etc.
Wal-Marts tend to be along high traffic areas so they make pretty noisy campsites. I try to find small small state parks, etc if possible. They are generally safer too.
I don't know where you live, but the east coast seems to be losing more and more of its "primitive" campsites (the ones without water and electricity hookups) to the RV style sites. They keep jacking the prices up to match. If you know where you are going ahead of time, you can find the USGS topo maps and they usually have the forestry service roads, etc on them- many is the night I've pulled down one of them and spent the night.
My wife and I spent a year traveling around the states in our Westie and stayed a number of nights at Wal-Marts. We popped the top with no trouble at all...at least no trouble from management. The problem we found was from noise coming through the fabric. We made the mistake of parking in back in Carlsbad, NM and spent all night listening to the rumbling of semi trucks. After that experience we opted to keep the top down for a better night's rest.
I'm generally not a big fan of WalMart, but on 2 occasions have stayed in their lot. No problem and they actually encourage it, as most people tend to pop in to resupply. The first time we were in Cal. and were late getting to our campsite and they gave it away and we had nowhere to go. The second time we were driving straight through but my son became very sick and we had to pull over. He had such a bad fever that he was hallucinating and falling out of the top bunk (hence the invention of the term "van diving"). It was a lifesaver, quite frankly. Here in the Yukon, where there is a constant stream of RV's in the summer, the lot always has 10-20 parked.
I have spen a number of nights in WalMarts. Not my favorite, but OK in a pinch. Some communities have banned it, and those places would be signed as such. Some are better than others. The open all night stores are the worst, because if a customer shops at 3AM he can't seem to find his car and uses his panic button to locate it. The semi's restocking the store typically drive though to deliver. So not aways restful.
I live in a 35' motorhome fulltime, work in National Parks, and travel between seasons. Bought the Westie for weeknds in the smaller campgrounds for fishing and photography.
Our most memorable WalMart night was after getting in to Guadalajara, Mexico at midnight and finding the only campground we knew about had moved and locked up (this in 2001). Wife is not a lover of the Big Box, but she was happy that night to find safe harbor. We pulled up next to the only other camper (big RV) and scared the H*ll out of them when we slid the side door closed. We were driving the old 68 "Porta-Party" so the door sound was not subtle.
I have recently returned from a long, cross-country trip. Stayed several times at Walmart Camperland. I did discover that several locations have decided to stop allowing any overnight camping. I asked inside a store in Minnesota and I was told that the decision is up to the manager of each store. Often, I saw signs posted at the fringes of the parking lots with a sign indicating that overnights were not allowed - with a drawing of a tow truck added for emphasis. After buying food, etc., inside the store, it always seemed like a fair exchange.
For me, after the curtains are in place it makes no difference where I am. Although I avoid the Interstate highways, (can't go that fast anyhow!) the rest areas are great places to pause for the evening. They are usually pleasant areas, bathrooms nearby, etc.
I think it would depend on the Wal-Mart. What they don't want is your awning to come out and your lawn chairs, barbeques, and carpets to be set out. But on my recent cross-country trip, they didn't seem to have any problem with RVs extending their bedroom areas, and since the pop-top is essentially another bedroom, I doubt that they'd have problems with it. That is assuming, of course, that the Wal-Mart otherwise has no problem with overnight camping.
To find out if the Wal-Mart in question allows overnight camping, go to:
It also doesn't hurt to actually go into the store and ask the manager. One manager in the Cheyenne, Wyoming store told us that while parking was forbidden in her parking lot, it was allowed in the parking lot of the Sam's Club next door. So we parked there instead. (And, yes, we posted our experience on that web site for future travelers.)