I have the older style comfort boiler which is heavier on gas than the new one, I have been saying for years that it's not just the cost of the fuel...the fact that it needs minimal electricity and just an annual service means the overall cost is less than most diesel heaters. I too have a solid fuel stove for main space heating but use the Alde for hot water when we are out cruising and did use it during the very cold winters a few years ago to warm the boat in the morning. One thing to bear in mind with the new model is that you will need a stainless calorifier and no copper pipes.
Cheers
Gareth