I'm pretty happy with how our multiplexed power system works. We have the main DC board with big CBs for inverters, solar, etc then from the main board we have 4 circuits running to the front inside of the camper, rear inside of the camper, the roof, and under the truck. Front/rear of camper handle inside lights, pumps, fans, chargers, cupboard/drawer locks etc. The roof does the floodlights, extraction fan, outside lights and the under truck does the compressor, outside pumps, ball valves for pump/filter, alternator, etc. Troubleshooting is quite easy and replacing the relay boards takes around 30 minutes (8 relays to a board).
The main issue we've had is the junction boxes outside leaking... doesn't seem to matter what I do water gets in there and then some time later the relay board is toast. I'm going to try potting the replacement relay boards next time this happens... hopefully that'll sort them out.