Yes, PCs are designed for sub-freezing conditions, but I am not sure what the lower limit is. All fresh water plumbing is inside where it is warm and insulated. But how cold it can tollerate depends on how well you maintain the warm interior. Also make sure all your outdoor storge compartment doors are fully latched to provide the best seal against the cold.
Be sure you have bled the water out of your outdoor shower. This is done by draining the pipes with the shower faucet open. Then close the shower faucet valves before pressurizing the system again.