If you go to the " Files " drop box , in the dark blue bar , across the page under the Google search box . Then to " Heating and Cooling " you'll find a document on furnace trouble shooting.
If the furnace worked before you removed it , and the fan runs when the thermostat is set , recheck the LP solenoid grounds ; and listen for the igniter sequence of sparking.
There should be a decal on the furnace that lists manufacturer and model number , Atwood owners manuals are a free download from the manufacturers web site.
This may help too.
Old link , no longer works , I'll see if I can find a fix.