Hi there fellow Tucsonan! You can leave it plugged in and charging as long as the converter has a "smart" charger. If it's a fairly new rig, it probably will have a smart charger, but you can read the information that came with your unit and find out for sure.
I have stored an RV in Tucson for the last 21 years, including the summer. I've never left a fan on, and wouldn't recommend it. The monsoons can hit in July, and driving rain can get inside your RV if you leave a vent or window open. Not only that, if we get a bad dust storm, you can wind up with a lot of dust inside the unit.