You've asked some really good questions.
As long as you keep the batteries charged I don't think you have to worry about freezing.
If you're able to keep the coach plugged in 24/7 than the converter would charge the batteries. The problem with the older coaches is the OEM converter isn't necessarily great for your batteries. You really need to look into how your batteries are being charged via the converter.
If you find the current converter isn't doing a great job you can get an upgrade on Amazon or someplace like here;
BestConverter - Converters, Inverters, Electrical Supplies, Electronics
If you had a process of charging your trailer batteries (assuming they were true deep cycle) that gave you about 6-7 years of trouble free use than that would work just fine with your rv batteries for the winter.
Running the generator for an hour or two really isn't going to do much for the batteries. The reason you need to run the genset every month is to keep the slip rings/etc clean. Consider yourself lucky if the genset is good and continues to work for you.