5rv with the highest R factors

The Heartland is a good choice. As stated elsewhere in this thread, just stating R values doesn't mean a whole lot sometimes. Heartland does test in the Dometic Extreme temperature testing chamber, and they pass the cold testing, as well as the heat testing. From personal experience in my Heartland XLT, it is easy enough to keep it cool in 90+ degree heat. It will be in storage for the winter months, so I won't personally conduct my own cold weather testing. However, it stands to reason that if it can be kept cool during the summer, it should hold it's own in the colder weather.