You can remove it and cap off the line. But you will lose the ability to filter the water that comes from your fresh water tank.
I only used the antifreeze once and decided it is too much trouble to add and then remove from the water system. I keep my trailer ready to roll year round and run the heater at 40 degrees in freezing weather do to 10 degrees without a problem.
Airstream recommends draining all the water out of your trailer for longer term storage. See the link below for detailed information.
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