I'm still quite a noob, and don't know any programming like you do already, so take this with a grain of salt, as I could be wrong
hopefully, the other much more knowledgeable people will help you with this, too. But, here I go at it

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I think you'll probably need to implement the ' scope ' codes, to get (some of) your desired results:
http://quest5.net/wiki/Category:All_Fun ... t_Commands----------
If the glovebox object is a ' child ' of the car object+room, then it should automatically not be visable when the car is closed (did you set the car as a ' closed_container ' ? And, of course the car must not be set as being transparent too, lol)
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ah, you set the car as ' openable/closeable ' , while my knowledge is limited, this is mainly for implementing a ' door or window ' type of object, vs an actual openable and closeable container type of object. So, maybe this might be causing you some problems, by having the car set as ' openable/closeable '.
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but, I'm not sure how the ' container types ' match up with the ' room and object ' setting, at how they interact with one another.
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I'm glad you're asking this scenerio, as I've tried to do a similar one, but had trouble with it, myself. Though, on trying a different aspect, that isn't included in your scenerio.
instead of doing the room description effects as you, I tried to implement a locked door along with it. So, for your scenerio example, include trying to implement a locked car door, requiring car keys to unlock+open the door, thus now allowing you to enter the car, vs being unable to enter the car with the car door closed+locked. Also, have this car door then be lockable+closeable and unlockable+openable from the inside of the car, as well as from the outside of the car, with the car keys.
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for your inside vs outside of the car descriptions, you'll probably have to have:
5.2 quest version = player <--> game.pov = 5.3 quest version
so, if using v5.2, then simply replace my ' game.pov ' with ' player '
if (not game.pov.parent = your car object name),
-> msg (outside of the car description)
if (game.pov.parent = your car object name),
-> msg (inside of the car description)
but, you'll have to figure out, or get help from others, on how to implement this with the room descriptions.
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an alternative method, if you're using v5.3, you can simply have the car set as being ' dark ', to hide the objects inside of it. having some kind of light switch or other method to then ' light ' up the car upon opening the door and~or entering the car.
http://quest5.net/wiki/SetDarkhttp://quest5.net/wiki/SetLighthttp://quest5.net/wiki/SetObjectLightstrengthhttp://quest5.net/wiki/SetExitLightstrengthhttp://quest5.net/wiki/CheckDarkness