RV Repair: Surbaban Furnace, propane tank, suburban service

Question
I have a 1986 Coachmen Crusader with a Surbuban furnace. It does not lite. The igniter sparks but aparently the propane is not getting to the spark. The propane tank is full and the regrig and stove lite with no problem.
Thank You for any help you can give.

Answer
There are several possible problems.

Thermostat defective
Thermostat wires broken or shorted
Limit switch
Blower relay defective
Wire off relay
Improper ground

Does the blower come on? what is the model#

Check out this site for general info on heaters.
http://www.atwoodmobile.com/Service/Trouble/default.cfm

This is Suburbans service page for heaters.
http://www.rvcomfort.com/suburban/service/furnaces_questions.php