Those videos are coming from a private travel company that isn't affiliated with the National Parks System. Quite frankly, it looks to me like you'd be spending $20 for a commercial for a travel company - and one that at least in my opinion doesn't look all that reputable.

The official national park website (linked above by dave) does have a ton of great information and it would be the first place I'd look. There are also a number of DVDs out there to help you get a preview of what you'd see, but I would look for ones produced by a more repuatable company like National Geographic or maybe the Travel Channel.

As far as a convertable goes, they will still have a trunk where you could lock your gear. It may be smaller than a standard sedan, so you might need to pack a little more lightly, but you should still be able to have security and the fun of a convertable, if thats what you decide to go with.