I just hooked my Deltran Solar Trickle Charger to the house batteries with cable clamps. When I run the generator every month, I take the rig for a little run. Not long or far but just to circulate all the fluids and move all the rotating parts and that keeps the chassis battery charged.
You could buy a latching relay and wire it in parallel to the chassis battery.
My battery disconnect is a latching relay that is operated by a single pole double momentary throw switch. Kind of expensive but it would work.
Easier to run the engine at the same time you exercise the generator.
By the way, this is on the back of my rig.
