I too had State Farm on our old gas motor home, as well as on everything else. We've been with them and the same agent since about 1974, when as a young whippersnapper they gave me a good rate on my 1970 Shelby GT500; nearly every year since I spend hours comparing other companys' offerings and quotes, and SF always wins out. Familiarity with the agent and vice versa counts for something, too.
But when we went to the larger diesel, State Farm just isn't in to that sort of thing, and wasn't competitive. Our agent didn't even try to sell us the policy and said there was better available elsewhere for less. We ended up with Camping World's version of GMAC, which is probably similar to what FMCA offers. We also got a Hartford quote, but as I recall the best money incentive required switching our other policies to them as a combo deal. Nevertheless, it penciled out best with the dedicated GMAC for the RV, State Farm everything else. Because we aren't full-timers, GMAC's option to suspend liability while the rig is home was a plus.
I did try to go with Overland when they first got on BAC's bandwagon, but although I really like the agency, the totality of features and cost just worked out better to stick with GMAC - at least for us, for now.
Joel