We could argue forever about what the critical climate conditions are that would definitely require winterizing. It comes down to these two options:
1) Do nothing and constantly watch the weather forecast to see if it is going to freeze, leave an unattended heater going which costs money, poses a fire risk and may not sufficiently heat all areas. You can then spend the wintering wondering if your lines have frozen.If they do, it will be a nightmare.
2) Spend six bucks on a jug of plumbing antifreeze. Take fourty minutes to drain your tanks and run antifreeze through the lines. You are now good to -50C and do not need to worry about mold or algae in your lines. You can then forget about your rig for the winter.
You decide.