Calvin, I found another wiring diagram, that I had down loaded, it was page 4 of the furnace info.
It shows 4 wires at the furnace bulkhead connector,
Red, cavity 1 +12v to the Tstat;
Blue, cavity 2 +thermo
Yellow cavity 4 not connected to the thermo
Green cavity 5 - thermo
These wiring colors may change between the connector and the T/stat, because Atwood did not supply the wiring.
If you only have 2 wires from your old furnace to the old T/stat location you may have to fish an extra wire through.
The way I read the diagrams I have, Red at the furnace to terminal 3 at the T/stat, Blue at furnace to terminal 8 at t/stat, and green at furnace to terminal 1.
I'm still working to get the Duo Therm A/C working, someone else has been playing with the wiring at the A/C and I think that that's what fried the T/stat. I'm proceeding with caution. $$$$