Doug,
What you should do is to spray PB Blaster into the arm at the base a number of times over the course of a day or two. While you are doing that, take the bolt that you removed and go to the local hardware store and purchase a 6 inch long one with the same threads and diameter.
Once the PB Blaster has done its job, screw the 6-inch bolt all the way into the bottom of the base until it stops. Then take a small hand sledge and tap upwards on the head of the bolt while another person is holding the plastic mirror head. It will pop right out of the base.
Then you have to disconnect the harness connectors. Now comes the hard part. That remaining connector may not go through the openings in the coach, etc. You may have to disassemble the connector. It should be a two-piece connector.
Now you can remove the mirror head and arm. Then remove the plastic cover that goes over the actual base. The metal base is attached to the curved sides of the coach and should be secured with four bolts two of which you can see in the one photo. Possibly the other two could be lag bolts.