Update: All systems work great, trailer performed as planned. Unfortunately I've sold the complete trailer, but I've decided to entertain the idea of building Hot Water Boxes for anyone of you that would want one, now that the design has proven itself.
Hit me up (PM) if interested, unfortunately the cost of the components can add up quickly so that might discourage some but as seen, it's a very cool addition to any trailer, truck, car, boat, dry cabin, fish cabin, hunting cabin....etc.