I would not go with Good Sam/GMAC.  I and others have had trouble with them raising rate for no apparent reason.  After you have been with them, you can expect to get a BIG rate increase.  When I received my renewal my rate went up over 60% with absolutely NO changes.  Same coverage, excellent credit rating, no accidents or citations.  They said that they 're-rated' my coach (what ever that means) which is why my rate went up. Others have had the same thing happen to them.  Here's a link to the posting that I replied to a while ago.  You should read the entire posting.
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/26598288/gotomsg/26598496.cfm#26598496