I came home from a long trip in October 2014 and changed the engine oil(synthetic) It has sat other than local trips to and from storage and to get maintenance. I have started it up every month or two...
When I went to Camp Freightliner and took some classes at the FMCA forum, I was told at both places to change the oil once per year unless you out a whole lot of miles on the coach. I recommend you change the oil.