Whatever width you wind up with, carefully check out and verify one thing: Make the most of the narrow coach width by making sure that the track (width) of the rear wheels is right out to the width of the motorhome's coach area. Don't go for a narrow coach with an even narrower rear tire track. You want a rear track width (where the bulk of the motorhome's weight is) as wide as possible for best lateral (sideways) stability - to minimize the leaning on curves, to minimize leaning on side-tipped small secondary roads, to minimize the leaning from the push of highway cross-winds, and to minimize the push of air from when a large truck passes you.
For reference, we have a short (24 feet) but wide (101 inches) slide-less and toad-less Class C motorhome that we drive everywhere - including going slowly and very carefully through some streets in San Francisco. However, we have the widest rear track width Ford offers on it's cutaway van chassis commonly used on motorhomes. Our rig uses the (optional for our motorhome's weight) E450 chassis instead of the E350 chassis usually under a motorhome of this size. The E350 Ford chassis has a narrower rear track width than the E450 chassis. The outside wall of the outside tire of our rear duals comes right out to almost the full width of the outer walls of the 101 inch wide coach.
Of course in cities all over the U.S., wide delivery trucks squeeze onto tight/narrow streets all the time for making delivery to stores and vendors ... but their drivers are very used to it and compensate accordingly.