I want to add a hot water recirc line to my trailer

You're right, the vent


I wouldn't intentionally dump the HW, but if some got in there, in the fall cool nights, it wouldn't hurt anything. I plan on shutting it off after it circulates, so the amount of hot to enter the tank should be minimial. But if we were in a very cold situation, having the ability to dump a little hot into the cold MIGHT be a good thing???