I've had the same dual Interstate Marine/RV batts for 9 years and can't tell them from new.
Its always on shorepower during the camping season, in the driveway or camping. After the last trip in the fall, I remove them to my unheated garage where they sit on a small automatic battery maintainer inside a box of 1" pink styrofoam board to hold their little bit of self-generated heat.
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