5W is very frugal; compared to your ave sized fridge is drawing 150-200W of power. Guess if the gasket seals at the door are still in good condition, it can keep the moisture out for a considerable period even if the power is cut...
Yes, the thing about the seals is true...never thought about that. Moisture will be kept out, but the other problem would be the stillness of the air. I thought that was one of the predisposing factors for fungal growth.
Nevertheless, I would hope that if I ever leave home for a period of a few days or weeks, I'd be carrying my camera with me. I'm sharing the cabinet with my Dad though, and I don't know if we'll be putting any other stuff in it...stuff that we won't take on a road trip.