Keeping two batteries happy (separated)

Well, here's the latest in my saga about battery separators. As mentioned the other day, I was going to just put in a manually (with a button switch) operated solenoid. The plan was to turn it on to connect the batteries when driving down the road and turn it off when parked. This would have allowed charging to the auxiliary battery (and refrigerator on DC) during drive times. Now I've decided instead to use a SurePower 1315 bi-directional "smart" solenoid. This will allow charging in both directions depending on power source--from the alternator to the auxiliary battery and from the converter (shore power or generator) to the starting battery while at the same time avoiding the issue of forgetting to disconnect the batteries. During long term off season storage, I'll disconnect both batteries from the separator to avoid whatever parasitic draw may be involved, if any. I do this anyway as a matter of practice when parking the RV for winter storage. The SurePower unit cost through ASE was a little over $50 so about the same as a high end solenoid.

Thanks everyone for the great discussion of this topic. I know that I have better insight on the subject now than before.