So, I believe you are telling us this dealer has had a trailer perhaps for some time. Now they have also properly winterized everything (for sure), and you are comfortable with taking the unit from a frozen environment?
So, they are going to give you a 30 day warranty from their shop most likely. Will you check it out in thirty days? Will you drive it back for 700 miles to fix the stuff that isn't working? No, of course you won't.
I bought mine the same way, I wanted that one, and it was February. I had a few issues, but a lot of experience, and fixed the gas on the hot water tank, and a couple of potential leaks on the roof. Tires were old and I had to replace them, but all in all, we are pretty happy with what we have. It's a super quality rig but.. they said it was winterized.. it was not. Could have been a disaster but our weather wasn't cold enough..
I would wait if I was you. Pick it up when you can check that everything works, not when it is frozen solid.