Whether the prospective water maker is a luxury or a necessity may determine some of the choices for you. We chose to cruise with two and use one underway and the other at anchor. The pickup for one is forward and in big seas it sucks up air so it is less than ideal for use underway. The other is aft and 4' below the waterline. One of our units is self contained and automatic, while the other is modular and manual. One runs off 240 ac the other runs off our batteries via our inverter on 120vac. Both output 35 gph at 78 degrees and use 1500 watts of energy per hour which equates 42 watts to make one gallon of Ro water. At anchor alchemy for us sometimes means a gallon of diesel turns into 70 gallons of drinking water in an hour. Nice luxury when everything is working but that doesn't always happen. 35 gph will require at least two long membranes and I'd avoid installing them anywhere near the engine as Hp can leaks can atomize the air with saltwater. Maintenance tasks such as filter and oil changes should also be a consideration during your design and install.