Do I need an external surge protector? Other essentials?

As for a water filter / system. It can't hurt. But, even if you sanitize and maintain your water system, you never know about the source of water you pick up. We use bottled water for drinking and usually for cooking. The water we load from who knows where in the on board system we use for showers, toilet, dishwashing etc. A clean water tank is great but you never know what you pick up on the road unless you are VERY careful.