I installed the Kuuma 11800, 5 gallon water heater. The previous water heater had the water connections on the top and the connections to the engine coolant were on the side towards the bottom. I could not find a similarly designed heater. The Kuuma has all the connections on the front face with choices of the feet on the front/back or on the sides . In order to have the heater fit and have access to the water and electrical connections, the heater had to be installed with the face/connections towards the engine compartment . The feet are on the sides rather than the front to allow room to move the heater around to make the connections. I was able to use the existing connections from the heater for the hot water lines. The water line from the water pump to the heater was too short and had to be replaced to make the connection. The coolant lines, which are heater hoses, from the engine to the water heater were also too short and were replaced.
Depending on how much you want the heater to run, you may want to install a timer or connect it to a switch. I am going back to install an on/off switch so the heater does not run all the time when it is unoccupied in the slip.