An update on this topic:
Last week I picked up a used 2010 Prius. It did a fantastic job of replacing the 1000 watt generator previously used for charging the batteries.
Test #1: Initially a 30 foot length of 14 gauge wire was plugged into one of the Prius 12 volt accessory connectors. This was directly tied to the cabin batteries (4 - 6 volt Trojian T105's connected to run at 12 volts). With the batteries sitting at 12.5 volts, and the Prius sitting at 14.1 volts, I measured 1/2 amp charging the cabin batteries. Not too exciting. I think that this is about what the 45 watt solar panel will do.
Test #2: Next I used a 25 foot length of 4 gauge wire I picked up on ebay, with an 80 amp in-line circuit breaker. Terminals were crimped on each end. I wanted to put an Anderson connector in there so I could readily disconnect things, but I didn't have a crimper for these huge contacts. So these cables were wired directly from the Prius 12 volt battery directly to the cabin batteries with the fuse in there. With these wires, 2.5 amps were measured going into the cabin batteries. With this configuration, the cabin was powered most of the weekend. The batteries charged up to 14.1 volts. At one point I saw them up at 14.4, which was surprising to me because I read that the Prius will only charge up to 14.1. I'm not sure, but it may be possible that the solar panel was pulling it up higher. For a while I tripped the circuit breaker and shut down the Prius out of fear that I may be overcharging the batteries.
There was one thing that I did not expect. I almost lost the Prius to my wife, who drove separately and wanted to stay longer. She insisted that I leave the Prius behind so she wouldn't have to run the generator. Fortunately I had an excuse: "But honey, then you'd have to take a wrench and disconnect those scary wires from the Prius battery and in the process, they might even create some sparks!" That worked!!
Next time I'll have to come up with a better excuse, or start looking into a hybrid for her, or a bigger solar panel so we can maybe eliminate the need for a generator entirely!!!!