I have a similar problem but it involves a BIRD and battery disconnect relay.
Instead of ordering replacements for those I'm waiting for the Amp-L-Start. It connects to the house batteries and charges the chassis batteries only if the house batteries are above 13.1. It is also supposed to prevent overcharging, simple install only three wires.
My house batteries are always around 13.35.
Will see when it gets here, hopefully in the next week. My chassis batteries are going down to 11.8 and I'm worried that is too low and will kill the life of them.
Chris