As for the freezing issue, it really depends on how cold, and for how long, it gets. If temps are going to go below freezing for extended periods, then definitely get those cans off. But more importantly, you should be winterizing all the plumbing
and most importantly, the engine heat exchanger
(raw water) system.
As for the battery
question, it really depends on the amount of solar you're going to get. I suspect you'd be fine leaving it connected since you're way down south there. I tried the same thing one season up here in Ontario
, and came back to dead batteries
in the Spring.