I installed a Chinese diesel heater in the spring, it works great, I've probably run 10 L through it so far and its been on lots. A few install notes:
-I suggest you mount the heater as high as possible and run the exhaust down towards the exhaust fitting. Walkaround configurations usually fit them right beside where the passengers elbow would be if they were sitting in the passenger seat. Consider serviceability and as few exhaust bends as possible. I spent $200 on the heater and probably $500 on exhaust parts.
-install CO and smoke detectors in the compartment the heater is fitted into
-use copper tubing for fuel line so it doesn't melt and cause a fire
-buy the highest quality exhaust components you can, they will see some salt and if they fail you've got 400*F gas and carbon monoxide in your boat.