You are basically running the engine under ideal conditions. Running daily, getting the temperature up, and not putting it under heavy load. I would not be at all adverse to going 200 hours between changes, with the synthetic if you are keeping mostly to the displacement speeds. If you had do, and were always staying to the displacement speed, maybe more. But with an extractor, changing the oil is not hard. Lots of oil adsorb pads to soak up the oil spill from the filter probably every other change--again assuming the lower speeds.
There are plenty of oil disposal sights at almost every marina (fishermen change their oil regularly.
There are plenty of oil disposal sights at almost every marina (fishermen change their oil regularly.