A full gas tank help prevent condansation, and helps to keep the fuel fresh. It also helps to reduce the chances of varnish and gum from forming in the tank....so if it longer than a month, consider useing fuel preserver to aid in keeping it fresh.
Keeping the battery connected and fulley charged is IMO the only way to go. Some have had problems with the engine imoblizer....the anti theft protection system, when the car is de-powered for too long. Even a fulley charged battery will get rundown when a car is in storage amazingly quickly.