My 72 Winnie originally had a heavy duty relay that was meant to tie the batteries together. Would give you an extra boost to start, and charge the house batteries off the chassis alternator while traveling. The power to the switch is also off the ACC wire from the starter switch, so when the key switch is off, you can't accidentally keep the relay on and run the chassis battery down.
I originally was going to replace mine with a solid state isolator, and I would have, had I not redesigned the system.
Instead I added a second HO 250 amp alternator that charges my house batteries.
I did add a cat master switch that I can tie the chassis battery to the house batteries, if I have an alternator failure, or chassis battery issues.
1972 Classic Winnebago / Brave D20
Dodge 340, 727 Tranny
2 Alternators, one is a 3G Re-Wired 250 Amp
Auto Transfer Switch with 3000/6000 Inverter
128 Watts Solar / 500AH Battery Bank