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There is no reason I can see why a G27 battery would not fit.. just make sure the battery you get does not have a CCA rating on it.. those are not true deep discharge batteries and will have a short life in an RV.
2004 Chev Silverado Duramax optioned past the max. 2009 Jayco Eagle 308 RLS 765 watts of solar, 6-6 volt batteries (696 amp hour), 2000 watt (4000 surge) whole house inverter.
140 days boondocking in 2016
211/2015, 196/14, 247/13, 193/12