Update....
We went to get the Chinook again today. Again it wouldn't start. This time I did check the voltage gauge before cranking it and it was very low. So we did the boost from the coach batteries and that worked fine.
We drove it to an Autozone about 20 minutes away. When we arrived I turned it off, started it again right away, no problem. The autozone guy brought out a tester. He said that when I started it, the battery dipped to about 8 volts. As it was running, it sat around 12 volts. He said that he'd typically expect to see it charging at 13-14 volts but this wasn't. Whether that was the fault of the alternator or whether the battery was too old to charge well or whether corrosion etc. were not letting it charge well he couldn't say.
So I bought a cleaning kit, got it home, cleaned the terminals etc. and started it up. Works fine, battery seems to recharge...but then, I expected it to. We'll give it another week I guess.
Thanks again for all the suggestions!
