Another vote for getting the bigger A/C.
Our 31 footer barely stays comfortable with a 13.5 unit if there's no shade and temps get up in the mid 90's or higher.
I'd also say to just let the dealer do the WDH install, just specify they need to install a good hitch and a good brake controller (Prodigy 2 is plenty sufficient IMO). I let our dealer put in what they picked out and, while the hitch was a Reese dual cam, I got the cheapest basic POS timed-based brake controller.
They do this hitch setup work all the time and can set it up right on the first try - worth a few hundred bucks difference when your spending 20-plus-K anyway.
