I know this is going to sound like I'm treating you like an idiot (not intended that way at all) but make sure you have the temp turned up to the point that it'll actually kick on.
If it's still not working it sounds like it's definitely need to be looked at. Also the fan set to auto still won't turn on would mean it's not right, that should come on no matter what.
Same year same trailer in my driveway and we love it, no issues with the furnace. Worst thing about it was the bed and bathroom faucet, both of which have been replaced with something worth using.