Anything other than a basic digital is pretty much overkill for an RV. The popular digital thermostat for this upgrade is the Hunter readily available at WalMart for about $22. It's easy to work with and the upgrade is straightforward and fast.
for basic instructions.
Do a search here on "hunter" without the quotes and you'll several threads in the Modifications forum discussing this upgrade in detail.
A tip: the wiring colors may vary. What you have to do is make a note of how your old Duotherm is wired and then match those connections to the new thermostat. Lots of discussion on that in the Mods section.
If you go with the Hunter, I can not emphasize enough that the +7.5 volt wire is taped off and not used. The Hunter uses AA batteries and that is all that is needed.
'12 F250 4x4 Super Duty PowerStroke 6.7 diesel
2011 to present: '11 Cougar 326MKS
1999 to 2011: '99 Sunline T-2453
Amateur Radio kd2iat monitoring 146.52