After winterizing, blowing out lines, then anti-freeze we just leave the filter off until we de-winterize. A little water in threads and cold will crack the filter in a heart beat. Bottom line, if not using the unit in winter, just leave the filter off. That filter is not available at lowes or HD, only can be purchased from water pur or from FR, or maybe a RV dealer.
2011: 54 days, 2012: 218 days, 2013: 175 days, 2014: 196 days
2015: 188 days, 2016: 72 days,
2009 Berkshire, 390QS, and toad