I focused on the water tank vent today. It is nothing more then a copper rough in fixture and the strainer from a faucet. I used JB weld to attach the strainer screen to the copper (after cutting off the end to size).

It will exit the side of the trailer under the stainless steel clam shell cover. This will allow water to flow easily, and when filling, it also lets you know when the tank is full.
Making the Water Tank Vent