The issue with boat heating is when you do have one that warms the boat up nicely the bi product is condensation which can equally be a pain, with little to no insulation and gaps around the window frames and roofs your fighting a loosing battle from flicking the switch! The best system in my opinion to have on a boat is a wet heating system with radiators.
Reading between the lines i think your biggest issue was your hire yard and from their response to you I think I know who it was.
When you hire a boat of any description everything should work, no excuses at any time of year. Having taken a boat out once with a blocked shower drain from the same yard it sounds all to familiar!