Good place to sleep through the night in a rental car...?

So...I'm arriving in Guam at 1ish in the morning, flying out about 20 hours later, and planning on renting a car. Anyway...I'm not opposed-opposed to getting a hotel room, but... I'd be just as happy sleeping in the car if there's a good, safe place to park it. Anyway, that brings me to my question: can anyone out there recommend a good, safe place to park my car, roll down the windows, and sleep through the night?

Thanks!

A blogger I follow spent a week doing just that...apparently it's wise to avoid the Kmart in Tauming

http://carolinetakesflight.wordpress.com/trans-poet-ation/the-100-oddest-places-to-spend-the-night/