Hi Randy,
I would rather you get it from the source if possible, Is it Dometic? I bought a round Dometic thermostat and had to change the electronics board up in the rear A/C cavity. I had to call Dometic for a clarification. It is quite a job, even for someone that does it all the time. Now, yours may not require the board change, I don't know. If you are adding an A/C unit, ??? Others will probably help on that.
Make sure when you order it, give them all the info you can. Model number, serial number of original unit, model and serial of new unit. This will be needed for a good match-up.
Here is my thermostat change slide show:
https://picasaweb.google.com/Jimsue1...eat=directlink