Tillerpilot battery draw.
I have the WP30 on my H37C. I have watched the battery draw while sailing and would be concerned with only one battery. But it seems that you do not need the battery for starting your outboard engine. Or do you? And it is a matter of how long you plan to sail under autopilot. I probably use six amps per hour. But my house bank is over 300 amp-hours.On my WP30 I have the bias adjusted so that it does not "hunt". In other words it can go off course for several seconds before it corrects. This helps the battery a lot. It might actually use amps only fifteen seconds in every minute. Maybe the WP10 can similarly be adjusted.