We selected the Raymarine SPX-5 Tillerpilot to tie into the Cape Horn Windvane with rope cabling - below deck.  Although the first choice was to be a very robust below deck Autopilot from Garmin, Cape Horn was able to show me how little effort is required (therefore a relatively inexpensive Tillerpilot can be used instead) when tied into the small arm that is provided by Cape Horn (mounted inside the transom - on their windvane).

We also purchased a Raymarine P70 Head to control the electronic Tillerpilot and it will be tied into our NMEA 2000 system.