I got my Volvo 610 wired up to supply all signals and voltages (except the backup light) to the RV. Tested it this weekend and it works. Turn signals flash while the brakes are applied. Flashers work. Many thanks to Dave (Oldphoneman) for his help.
The central item in this design is the Hoppy Power Taillight Converter model 46255. Not all taillight converters will work but this one does. Picked it up at Pep Boys for $39.95.
http://dsimpson.home.infi.net/Volvo_RV_Interface.html