You will still need to stabilize the gas. Sta-bil and similar products keep the gas from prematurely turning to a varnish-like substance (I don't know the actual chemistry involved.) Products like HEET are supposed to take care of the moisture problem but I've got my doubts about how well they work. Vehicles that are regularly driven will not generally develop moisture problems. If I had a car that was kept idle for long periods of time I would definately keep the tank full, as I currently do with my small engines and gas cans.

Edit: I should probably add that I live in a desert. It is possible that people in extremely humid climates may have to take more precautions against moisture in their every-day driver than I do.