Can I just empty water tanks instead of winterizing?

You can do whatever you like, it's your rig. Two years ago I returned from Florida at the end of March. I drained everything and ran a heater a couple of cold nights. End of April I was going back south, why waste the effort.

Well I ended up with a small crack along the threads of a plastic sediment bowl on the water pump. Ended up having to replace laminate flooring. If in doubt play it safe. A ounce of prevention is still worth a pound of cure.