x2... remove the internal and use external. I never even installed the cartridge that came with the unit (still in the shrink-wrap) and use an external carbon filter on any water that goes into the unit (either city water or into FW tank). One benefit is that the system volume is going to be a whole lot less when pumping in winterizing antifreeze (and when trying to flush it all out).
2015 Rockwood Signature UltraLite 8282WS Platinum, GY Marathon LRD, TST 507RV TPMS
2005 GMC 2500HD CCSB D/A, Curt E16, Prodigy P2, Garmin RV760LMT w/BC-20 b/u cam