You will want to go join the Tiffin RV Forum.
http://www.tiffinrvnetwork.com/forum/In the meantime, there is a known issue with the IR repeaters in the coach and Dish receivers. Some say it simply will not work and others say it works OK.
You will need to located the IR "eye" in the cabinet and try a few different locations on the receiver right on or around the location of the receive window on the receiver. Using a clear spacer (plexiglass?) has been reported to help as well. The best first hand info if available there but that will give you a couple of things to try.