I’m not sure you need to spend money on a monitoring system. It might be a safer and smarter decision just to shut off the battery when not in use. That way you don’t have to worry about it being overcharged or a fire if your converter decides to melt down or even phantom draws. It also renders the trailer jack inop which is a nice way to slow down a trailer thief.

Btw our most overlooked phantom draw is the powered roof antenna, the on/switch is behind the TV and often forgotten.