Congratulations on your new coaches...
Be careful with your auto LP switch, unless it signals somehow that it switched, you won't know it, and end up with two dry tanks!!
We had an older model trailer that would draw from both tanks, if they were on, and always kept one closed for this reason.
Your so right about the 12v drain. Our 2007 T-276-SR has a master disconnect switch on the front frame cross member for that reason. We are fortunate to be able to keep the trailer plugged in so we don't have that problem. Just check the water in the battery every couple of weeks.
Our dealer told us to make sure we open the awning every once in a while to let it dry out. They do get condensation in them and when you get a sunny day, not a bad idea to open and air it out for a couple of hours.