This is a great thread!
Although I don't have much first hand experience with car camping for skiing, I've got some other insight you guys might find useful (I could probably write a book about how to scam some kind of indoor shelter @ Copper.)
Here's some ideas relevant to this thread:
1. Car camping @ National Forest trailheads is about the safest place to be unless it's specifically posted NOT to camp there. If it's posted, there's a good chance cops patrol that trailhead regularly. A lot of ski areas have trailheads very close by, some even on property.
2. HR is your friend. I've never done this, nor have I heard of anyone doing this, but I bet it could work.. Apply for a job at the resort. Probably a manager position or just anything to get an interview - it's usually Really Easy to get an interview. Ask HR if they have any employee housing available you could stay in the night before your interview. Stay in the lodging, blow off the interview. Of course, this only works at bigger resorts with real employee housing.
3. If you want to car camp at a bigger resort, don't stay in the giant, main parking lot. Find the 'pay' lots during the day - usually at night they leave the gates up and it's actually OK to park there overnight. Again, mind the plows. It's almost always ok to pull in at night and leave your car there during the day while you ski. A lot of resorts offer 'free' close parking to employees if they arrive before 7am or 8am when the gates go down, so your car would just be mingled among those.
4. 4 words: Heated Underground Parking Garage. Even if you need a parking pass, there's a good chance you can park there at night without anyone caring. You just need to pull in later in the night. At Copper, stay in the Passage Pt garage, the Tucker Garage or maybe Copper Springs (this one has cameras in the garage, but they're generally not monitored.) However, don't try to get away with this during the day anywhere. Property managers are on the prowl during the day trying to catch the day skiers trying to scam close-in parking. At night you only have to deal with the Security staff and they're way too busy hitting on the girls at the front desk to bother wandering through parking garages.
5. Hot tub rooms kick ass. Getting into a hot tub room isn't that hard - just follow someone into the building (preferably a condo building, not a hotel.) Then just look for the sign that tells you where the hot tub room is. If you don't see a sign for it and don't want to look like an idiot wandering around, go for an elevator ride - it's probably posted in there where it's at. Carry your duffel bag in or small backpack in (don't bring your full-size backpacking pack) and then start looking for the bathrooms that'll be nearby to change in. There's often showers nearby too. If you're going to try a hotel, go for the biggest, older hotel you can find. You're really looking for something like a Holiday Inn from the 70's. There's usually good bathrooms easily accessible and the pools/hottubs aren't viewable by the front desk staff.
6. Someone else mentioned camping near bars - don't. Walmart parking lots - don't. Anywhere with glaring lights - don't. Someone can and will notice your windows fogged up.
7. Speaking of which, RainX makes an anti-fog wipe that I've had good luck with in my friend's mini-van. Wipe the inside of the window with it before going to bed, no fog on the windshielf in the morning.