Since you have the fan on, I suspect you've found the thermostat and have turned it on.
My uneducated guess as to why there is no heat is that you have a pilot light that is not lit. My trailer has electronic ignition, so that's not a problem with mine, but I think the older trailers may have had pilots that you have to light manually.
Look for the exhaust pipe on the outside of the trailer. You should have one for the hot water heater and one for the furnace. They probably will be in different areas. Once you find that, I'm going to guess that if you take off the access panel, you'll be able to find the pilot light, or, figure out why it's not lighting for some other reason (spider webs in the gas tubing, etc.).
Hope this helps. Glad to have you with us.
- Jack