Good question as I have pondered the same. Called Winnebago and they simply gave me a list of the dealers in SoCal and wasn't impressed. They highly recommended Altman's but unfortunately they're gone, I was told.
My coach is way out of warranty so I'm going to give Bill's RV Service, (Bill Gehr.com) a shot in Ventura. Have talked to one guy who bought his at Barber RV in Ventura and was satisfied with their warranty service. Not knowing where you're willing to travel, that area might be a stretch.
Redlands Truck & RV is tops for the chassis stuff and have used them for quite awhile. I think Keith has a Winnebago so maybe he can recommend a dealer.
Let us know who you choose and what your experiences were.
Congrats on your new coach!