Touched base with a heating engineer who happens to live on the marina. He has just qualified (as I understand it) and has been trained to put LPG heating systems into boats. Handy. I had contacted Calor before but they were difficult and moaned a lot that they had not done boats before.
Will be setting up a meeting to go over the various ideas I have had. Will keep you updated but handy to have someone who is both recommended and on site as it makes the whole process much simpler.