Give some serious thought to whether you really want reverse cycle. Read what Flagship Marine has to say on the subject.
The only advantage of reverse cycle is better efficiency when the outside water is within a fairly narrow range. And, the price you pay is more complexity in the unit, with greater chance of failure.
With a heat coil you can run the heat and fan even out of the water, a big convenience for those who work on their boats (or just sit on them and have a beer) when on the hard.
If you are not paying for metered power (my marina lacks individual slip meters) then there is little reason to put up with reverse cycle.
1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida