Here is a link to the Installation Operation Maint Guide
for the split systems.
It does have a winterizing section and deals with both the raw water loop as well as the chilled water loop. There is a need to wintereize both but it states the antifreeze can be left in the chilled loop under normal operating conditions.
I'm not familiar with these as mine are self contained... however, if I understand how they work correctly the ER unit is the chiller unit uses raw water and contains the compressor & condenser.
The air handling units are separate and the cooling / heating is provided by a recirculated "chilled" fresh water loop. This also needs to be winterized w/ AF.
This is similar to an industrial / commercial heat / AC system that uses a heated / chilled water loop to multiple zones / air handlers.
The info states that the recirc loop should include fresh water make up source (from boat FW system?) I'm thinking that you MAY be able to add AF to the recirc loop, close the make-up and run the as long as the raw water loop including inlet & outlet AND any make up for the recirc loop are in heated space. (you may need to check / top-off the recirc loop periodically?
I'd suggest you confirm that this is really what your set up looks like and maybe talk to the mfg tech help line to confirm ability to run the system w/ AF in the recirc loop as long as chillers are in heated space.