Here is the one I used, doesn't look like Costco has it anymore but it is available at amazon.com
http://www.amazon.com/dp/B00654MFXU/ref ... B00654MFXU
This has a back plate about 3" x 3" that I superglued 3 small earth magnets to. When I park I put this on the van to the left of the awning, the light and motion sensor is adjustable, it is very bright. Also, being so cheap, I'll pick up another. Thinking about using it when parked in my driveway too for security.