I have only experience to share about an engine
drive with a ss holding "plate". I find this works well and does not consume amps... though chilling is only talking place when the engine
is running. However, running the engine ALSO creates hot water
and recharging of the batts, powers the windlass
and the boat when not sailing. I find the system works well. I installed it from parts
... not easy... but with the right tools and patience.. doable. We don't stay on docks with shore power
so the engine drive refer w/ holding plate seems the way to go. The plate is a freezer
one enabling the box to be brought down very cold if we want.