On my recent 25-day road food trip to Colorado and back, I spent about $1,800 on food and gas. For the whole trip, I spent exactly $50 on accommodation. And I did this in October, when many of the national forest campgrounds, which would be cheap or free, were closed.

Did I mention I did this in October, often at high elevations and during a couple of early-season snowstorms? One early-October night in Laramie, Wyoming (7,165 feet), the temperature plunged to -8 Celsius (18 Fahrenheit). I had no motorhome/camper or even a winter sleeping bag and tent to keep me toasty. Indeed, I slept in the back of my Toyota Matrix, sliding the passenger seat as far forward as possible, inflating a Thermarest mattress, then crawling into a three-season sleeping bag and stretching nearly fully out. So how did I manage this, paying for camping at only two state parks and one KOA, as well as staying a few nights at a friend’s place in Colorado?

Thank you, Walmart! Many of you who blithely plunk down your plastic at comfy motels and hotels may be unaware that this bastion of retail capitalism allows free camping (formally known as “overnight parking”) at many of its stores. I think it started as a corporate gesture to customers, plus it doesn’t hurt that campers crawling out of their RVs in the morning are likely to head inside and buy some bananas, milk and maybe a t-shirt of the local college football team.

Over the years, there’s been a bit of a backlash, mainly from municipalities that don’t want overnight parking in their jurisdictions. I’m not sure what their problem is. In my experience, it’s mostly older couples pulling up in RVs and never coming out, other than to water the requisite dog that goes with these houses on wheels. Maybe these cities have been lobbied by RV park owners and the like who feel they’re losing business.

In any event, some Walmarts allow overnight parking, others don’t. Walmart doesn’t even officially acknowledge the practice on its website.

So how do you find out where overnight parking is allowed? Start by checking this website, which often indicates which Walmarts don’t allow overnight parking. When you drive into a Walmart parking lot, you can also look for signs warning of no parking, hefty fines, towing, blah, blah, blah.

I use two methods for checking. If I see a number of RVs in a corner of the parking lot, I figure it’s probably okay. To avoid having someone with a bright flashlight knock on my car window in the middle of the night, I also go into the store, wait in line behind the people returning TVs and cartoon-character pajamas, and ask at customer service if they allow overnight parking (I’d advise against using the word “camping”). If they do, they’ll usually tell you what corner of the vast parking lot they want you to park in.

So what’s it like “camping” in a Walmart? I would say the vast majority of folks who park there are in RVs and are thus cocooned in their little aluminum world, with a curtain pulled over the front window and the TV on. I, on the other hand, sleep in the back of my car and am thus completely exposed to the Walmart parking lot elements. Let me tell you, it’s a different world out there, with guys fixing their beaters, getting into exuberant arguments and entering and exiting the parking lot in strange loops rather than taking straight lines.

One guy, when backing out of his parking stall, booted his rusted junker and would certainly have crashed into my parked (but unseen) car if I hadn’t honked. I doubt he would have left a note.

All but one of the Walmarts I stayed in was open around the clock, so there was a constant parade of vehicles coming and going, with some drivers unable to resist the urge to floor the gas pedal on an unoccupied stretch of parking lot. Motorhome generators and idling semis added to the sound mix. I also experienced a little sweeper truck that must have made a dozen circuits of the parking lot throughout the night, often hovering a few feet away to remove little bits of dust…. or vomit.

It’s not exactly dark in a Walmart parking lot, either. In fact, you can almost read by the glaring, high streetlights. As well, there are flashing lights from the all-night security vehicles, or from police cruisers that perform the same duties at some stores.

So how do you actually sleep in such an unpromising environment? Good earplugs and an eyeshade are essential. I actually had some pretty good sleeps, once I got used to things, though not as sound as in a darkened, quiet campground.

The biggest problem was just killing time till I was ready to go to bed. This mostly consisted of writing food notes on my iPad in the car’s front seat, listening to NPR’s coverage of the U.S. election and wandering the aisles of different Walmarts. Occasionally, I’d go to a brewpub for a pint.

The idea was to get to bed no earlier than 10, so that I could arise eight hours later and head into the store for a pee and maybe a quick, furtive hair wash under the tap. Then it was time to head out, in search of a good breakfast place with early opening hours.