I've heard that many have replaced their thermostat with a Hunter instead of going with the Dometic digital as the Hunter is easier to use and set. It's also available at more places for a lower price than the Dometic digital. Somebody said you can buy it at Walmart for $20. I'll take a look and see if it's still available for that price at Walmart.
Attached is a wiring image from the Heartland forum somebody posted.
Heartland forum thread: click
Here's another blog post that may be more detailed: click here
Here's another thread on the Keystone forum: click