I'm about to change out the chassis batteries in our Allegro. It has Interstate 31-MHD batteries now. They are original to our 2012 model so I'm thinking they were installed in 2011 making them 5 year...
AGM actually is superior (compared to flooded) for just sitting with very low self discharge. Also charges faster when you do roll the RV. Still need to take precaution against any parasite drain while in storage.