As far as your two banks being different voltage, well yes if one is gel and the other wet, or similar combinations of differing battery types (gel, AGM, wet) but if they are all the same whatever that is, it works fine.
Check BNO's archives and there is a LOT of discussion on this topic. Same applies to 24 volts as applies to 12...
Brian,I agree with most of the above, particularly the battery issue. The main difference between a starting battery and a deep cycle battery is the thickness of the plates and some of the chemical reaction issues in the charge/discharge cycles. But the reality is both the house batteries and engine batteries will charge fine when running on alternator. I've never had one set of batteries last significantly longer than the other in 20 years of RVing and 42 years in electronics.I've had solenoids. I've had solid state (diode) isolators. I've never had either fail except in an early rental unit in the '70s. Simply, the solenoid used by the RV manufacturer was way under-rated for the load and not a "continuous load" design.I'm using a solenoid that is smart (off, auto, manual), has a CONTINUOUS load rating of 500 amps, and costs only $150.00 from Newark Electronics (www.newark.com).I'm having a senior moment and can't remember the mfg name, but I can get it Monday if you're interested.The unit is smaller than a coffee cup. Compare that with a 300 amp diode isolator in size and price. Chuck Newman