I have a cabin in northern Minnesota where I keep the temperature at 50 degrees in the winter when we only get up there occasionally. I want to set up an emergency heating system in case the heat goes off and we cannot get back up there immediately. (I have an emergency sensor that calls if the temp drops below 50 degrees, which it would have done had we not been up there at that particular time when my gas furnace blower fan shorted out!) I plan to hook up four used eight-foot baseboard heaters in the basement that will draw about 35 amps on a 240 circuit, connecting from the electrical box to the units with 10ga. wire protected with a 40A circuit breaker. I am looking for a thermostat that will trigger under 50 degrees that will handle this amperage.
Is my plan sound, and do you have any suggestions on a thermostat?
Thank you.

So you must have a hard telephone line year round, right? There are systems like your that do more than just call. Not sure if the Ezra Group (http://www.ezragroup.com/) still sells their Talking Thermostat or the Commstat CEM but I have one that I can telephone and change the temp or start/stop a heating system. Or you can install a Honeywell TL8230A1003 -  $49.45 - Honeywell - Programmable Double Pole Line Voltage Thermostat for electric baseboards - TL8230A1003 (http://www.pexsupply.com/product_dtl.asp?pID=4082&brand=Honeywell&cID=399) which can be set as low as 40 degrees. The only shortcoming to your plan is most furnaces should not be set below 55 degrees or condensation will build in the heat exchanger.