Marin have you looked at the espar?
The biggest issue in a boat like ours is where to put the heater. For example, a bulkhead-mounted Dickenson propane (or oil) heater would work well in a boat our size but there is no place to mount it. And while GBs have a fair amount of stowage space, we have none that we want to give up for the installation of a heater.
So the best solution is a diesel heater mounted in the engine room with either forced air or hot water circulation sent to small outlet units in one or more cabins. Fuel would be taken from the boat's fuel tanks. While the components themselves are not all that expensive the labor to install them can be. And I don't have the time (or the desire) to do this sort of installation myself. From talking to other people who have had similar systems installed in similar-sized boats, the cost with installation hovers around $7,000 give or take.