(I'm in the coolant industry)
a. You REALLY do not want to be adding and SCA filter to an engine unless you plan to closely monitor nitrite levels.
There is also very nearly no chance that you need SCAs (assuming you are using long-life coolant) unless you are a work boat running 24/7. Over treating with SCA--whether through filter addition or liquid addition is worse than no SCA.
b. SCAs are only needed every few years in very heavy use (1000 hours with heavy use). The greatest chemistry risk, by far, to marine
coolant systems is a tiny seawater leak. The condemning limit for chloride is only 50 ppm (seawater is 23,000 ppm), and thus most manufacturers recommend changing the fluids every 2 years, long before SCA is needed.
c. If you are seeing actual rust, you have another problem (stray current
or an air leak--air is deadly as it contains oxygen) you need to solve. You do not need a filter.
d. ALL of the truck OEMs are moving to nitrite-free coolants (no SCAs) for a number of technical reasons (nitrite can form ammonia insitu in vehicle systems). Go to a nitirite-free heavy duty formulation and say good by to any thoughts of SCAs. Simpler.
e. While liner caviation is real, I think it is a tiny problem for small marine
engines. This is usually seen on large turbocharged engines, often at higher altitude (lower pressure). And it will not be a problem if you change the coolant every few years. Not a flush, just a change.