Couple of things about HOU.
There are EcoPark spaces that are within a short walking distance of the terminal. They are uncovered, though. You enter the terminal on the ground floor and have to walk down a hallway to the baggage claim area, and then go up to security.
BF's co-worker had his truck stolen out of the HOU Ecopark lot a couple of months ago. He thinks it happened within minutes of him parking and heading into the terminal (basically, there are people waiting).
He found out because the thieves tossed his OnStar and personal effects out onto the road near the airport. Someone walking found his stuff, and there was a business card mixed in with it. The person called the number on the card, and after a WTF moment, he figured out his truck was stolen.