If there is a vent on the fresh water tank itself, there should probably be a hose going from it to the vent on the side of the PUP. You can switch the fridge to 12V while traveling but be aware that the fridge uses quite a bit of current and you should make sure that the 12V aux connection in your Bargman plug is powered and has a heavy wire from the fuze box back to the plug. Also if you stop during the trip say for lunch, be sure to disconnect the trailer plug as it can drain the tow vehicle battery. If fridge is cold and contents are cold you should be OK without powering fridge.
2015 Freedom Express 248RBS
TV 2015 Silverado HD2500 Duramax
TST Tire Monitors
Honda 2000I + Companion
2 65W solar panels