I don't know what year Thor freedom elite 26E you have, but the ones I found on line say they have a forced air LP gas furnace of 25,000 or 30,000 BTU. Check that gas is on, (does your stove and water heater work?) and thermostat set on heat. If someone stands outside next to the furnace exhaust as the thermostat is turned up, you should hear the fan motor start up. When the fan is going fast enough to push the paddle of the sail switch, it should turn on the gas and you'll hear the clicking/sparking of the ignitor.
Take the cover off the furnace and write down the make and model number. If you do a Google search of that information you should find a PDF manual and trouble shooting guide to download. You could also do this with the other systems and appliances in your RV, it's a nice reference to have.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI