Keep in mind, the closer you are to the max the worse all around performance would be. We have a Minnie Winnie 2201DS that is 5k dry and 7k fully loaded and a 2012 Expy. Limited with HD tow and a WD hitch. My wife and I plus 4 dogs.
Going across the Rockies the uphill performance was glacially slow (had to use the truck lane) -- going downhill we definitely stopped and let brakes and such cool down. Even going across the Appalachians uphill performance is less than stellar. In Florida where it's flat performance is fine and I could probably tow right to the max.
Our average trip mpg is 9-10 mpg towing at 65 mph.
IMHO, a dry weight of no more than 6500 lbs would be the absolute max if you plan to go anywhere. I also think, if you're going to do this full time, you need to seriously consider a pickup and a 5th wheel rather than the Expy and a travel trailer. Just my thoughts, but I have logged over 20k miles with this set up.