In my last post I was not referencing to the Raspberry Pi BMS, only the Valence U-BMS. It's also tricky that there are no standard CANbus protocol, different chargers have different protocols. I know the U-BMS uses the BRUSA CAN-bus protocol.
Instead of using a SSR, you should probably use a DC contactor to turn of the DC voltage from the chargers instead of the AC voltage to the chargers, and then another to control the load, or if your solar inverter have some built in switch you can trigger.
I am hacking my car, that's why I'm not controlling charge by a DC contractor, which is probably better.
How many batteries do you have? Series or parallell?
You could of course not use a BMS at all, as long as the chargers cut of at safe voltage. I would set that below the maximum om 14,6v, to not harm any cells if they end up unbalanced, especially if you have a number of batteries in series.
I have 3 batteries wired in parallel. 12V @ 414AH.
All cutoffs are at 14.4V. I have monitored my batteries for 2 months and they never go above 14.4V.
I am familiar with relays, but not DC contactors. I'll have to look into it.