I just left my local Ford dealer after they refused to service my F-53 ford mo ho on the grounds that it was too big. Now ths is not a old time Mom and Pop dealer, this is a dealer with multipal brand...
Keep in mind also that a Ford/Chevrolet/Dodge dealer are individually owned and operated, just a franchise and reserve the right to refuse service. I don't even think they need a reason other than they just don't want to do it.
Personally, working on RV's sucks. You would think being so large that there would be more room to work on them. Just the opposite, a real pain to work on.
Many shops around here simply will not work on motorhomes, period.