Cars are rare and valuable in the Wasteland.
There should be risk of losing them that is very real.
The tedium of tent alting/etc. can be considered an approximation of having to hide and camoflauge cars outside of towns.
In the event of Car Park implementation:
Guarded towns/mines/train stations could perhaps have "Car Park" added to the Map Preview screen.
Going to that map incurs a fee. To make the mechanics of fee payment simple, the fee is paid to a guy in a tollbooth/guard shack on exit. If you leave a car there a long time there will be a large fee to get your car back. One percent of vehicle price per in-game week, rounded up to full [in-game] weeks.
The car dissappears on entry, and you appear in a map instance with your car when you pay your fee. There are no exit grids in these map instances: you have to use your car to leave. You can always ask the gatekeeper to teleport you to your car ("I'd like to see my car") as long as you have time left on your week if you already paid. Maybe the gatekeeper would also be present on your map instance so you can use the trunk/do repairs without having to use your car to leave.
The big problem with this is that it is like having an extra tent. (Make it so ground items on these maps dissappear in 3 in-game days?)
Modified versions of the idea are to have parking spaces like hotel rooms, with doors and/or guards. Problem here is that people will fill up the map with caravan cars to grief. Also- where does your car go while buying your parking space?
A temporary row?
Perhaps after an in-game month (6-8 weeks?) of not paying, your car is dumped to World Map or put up for sale. (Based on Reputaton, Charisma, and Luck.)
Car contents may be confiscated in this case or can be bought back for a 10% fee (appears in Barter value as items are dragged onto the barter table, plus 1% per point of Charisma and Luck below 5, and minus 1% per point above 5. Also plus/minus 1% per level of Reputation- zero for Neutral, up or down for Accepted, Liked, Idolized or Antipathy, Hated, Vilified. Even better- accepted is 2%, Liked is 5%, Idolized is just no fee. Hated and Vilified is forfeiture- including the car being put up for sale immediately upon reaching that status. Antipathy would be double fee.
For sake of ease- the tollkeeper will not require caps and will credit full value for all item types. He only trades for confiscated items to avoid some kind of trading sploit.The tollkeeper will have many separate inventories to handle different batches of confiscated items.
A similar thing could be instituted for item buyback after being murdered in a guarded town.
Perhaps items acquired by tollkeeper would appear in inventory of some junk trader who is on Car Park map. This guy recognizes only one third (half?) value, modified by Barter, for everything. No preferred item types. It all gets converted to caps every in-game day.This trader also has all caps paid in fees.
Lockpick is not disabled and you can still be followed. This is in case you lose your key: you can lockpick or bring a lockpicker.
Yes there is griefing potential in this. Wasteland is harsh.
If you don't like it: For a 100 cap fee per time (plus 10 caps/level and 10 caps per reputation level/Cha/Luck plus-minus as above), the tollkeeper can hold your key.
Tollkeepers cannot copy keys.
@campers going for the Car Park caps: not only are their guards (and turrets at VC and NCR car parks), but actions on car park count as double karma hits. (You don't mess with someone's horse!)