Take a lesson from a certified mechanic I know, with decades of experience.
He had a large saltwater boat, berthed in Valdez, that he routinely used in the often treacherous waters along Alaska's coast. His boat had an onboard charger/maintainer for each battery bank, for plugging into shore power. (An appropriate use of the term.)
He also had an onboard genset and carried a small Honda generator in case all else failed.
In the fall, he would pull the batteries from the boat (as well as his RV) and take them into his heated shop. There, he would hook the batteries up to the $1,000 multi-bank charger/maintainer he had, with a separate circuit for each battery.
I'm not saying you should invest in that kind of a setup, but TreeSeeker is right. You should have at least two charger/maintainers, one for the coach battery and the second for the SLI (engine) battery. (And, pull the batteries over the winter and store/charge/maintain them in a heated garage or shop.
