Before I saw this question, I had no idea the term stealth camping existed, but I have definitely done it a number of times, just backpacking, with a bike, and with a car. Yes, it's possible to do stealth car camping.
I live in the US and most of my experiences have been in New England (where I live) and Arizona (which I visit every summer). New England and Arizona are quite different in what you are allowed to do and what people care you do. Regardless of all that, one thing I never do is camp on private property that is clearly marked to indicate the owner doesn't want you there. The owner has the right to make the call whether they want to allow others to enter their property, and I respect that. However, I take a somewhat different view with public property. I suppose that's just as wrong, but it feels different to me. I'm willing to sneak onto public property where I know I'm not really hurting anything or taking something away from others.
If you think you probably wouldn't be allowed to camp if you asked, it's a good idea to wait until dusk. One time I was on a multi-day bike tour and found myself a little north of Milford NH as it was starting to get dark. There was no public land around I could see. I found a patch of woods that was big enough to conceal me. I stood next to my bike by the side of the road making like I was drinking water until there were no cars coming by and snuck into the woods. I went in maybe 200 feet and set up my tent. It's a really small low to the ground brown tent just big enough for me to lie down in. There was no way anyone could see me from the road. I went to sleep and thought all was well.
In the middle of the night I heard people talking and walking thru the brush. I was suprised by that. It was the only time stealth camping I ever ran into anyone in the middle of the night that closely. They couldn't have possibly seen me, so had to be there for some other reason. It wasn't supposed to be hunting season, but I think that's what they were doing. Or more accurately, they were trying to poach, probably deer. I think they saw my tent or my bike and took off. I kept still just in case anyway. Apparently they were more worried about being found than I was. The next morning I got outta there as soon as it was light.
In New England, land is more managed and controlled than in other parts of the country. The rules in the White Mountain National Forest are pretty strict about where you can camp. I really hate public campgrounds because you always seem to get stuck between a crying kid on one side and a bunch of beer bellied yahoos on the other being rowdy until 2:00am. No thanks. The WMNF does have a few places that are undeveloped sites where you can just pull in and camp for the night for no charge. Of course there are no commodities, but that's fine with me. I'm just looking for a place to plunk a tent for the night.
Unfortunately, the legal free sites are scarce and usually fill up on Friday and Saturday nights. This is where you do stealth car camping. Find a trailhead parking lot to leave the car. The trick is to go in some other direction than the trail to plunk the tent. In the WMNF it is not unusual at all for a car to be parked overnight at a trailhead, so that draws no particular attention. But, you don't want to be caught with the tent where it's not supposed to be. However, nobody looks anywhere but along the trail, and they aren't really looking for illegal campers anyway. Going accross the road from the trailhead is usually the best, since nobody has any reason to be there.
In Arizona stealth camping is mostly pointless since there is so much public land and it's perfectly legal to plunk a tent as long as it's not in the middle of a road. I was used to the east, and the first time I went to a ranger station in the Apache National Forest to ask where I'm allowed to camp, it took them a while to comprehend the question because it was so foreign to them. Generally they don't want you driving off the road (although there are large areas where that is legal too), but otherwise if you're just going to plunk a tent they don't care.