DC to DC charger Question

The quick answer is
where the ground is located
isolated two comments are separate. Engine. chassis

Non- is both components are common, engine/chassis are grounded together

most common usage is two battery packs 1 in the truck 1 in the camper

So if I want to only charge the house I can seperate the chassis cable from the Bim225 and insert the positive to the chassis cable and pick up a ground from the house battery shunt?
Would it be possible to then hook an on off switch between bim chassis terminal and the positive and leave it in the off position till a boost would be needed?
I would instal a 120v battery maintainer on the chassis battery to prevent depleting it due to parasitic loads during camping.

Jay58,

Look at a Trik-l-Start. Ideal for chassis battery maintenance.

There are also relays that do not cut in until 13.5 volts is achieved.

I do have manual control of the charging solenoids for my house bank.

I don't think you would even need a BIM225 !