When the thermostat requests heat the furnace blower will come on after a delay of one to two minutes. The gas does not have to be on for this to happen.
Forest River likes to put the furnace and refrigerator on the same fuse so you need to check your 12 volt fuses and make sure the fuses are all in and there are no red lights on which would indicate a blown fuse.
According to the literature for your T T you should have a digital thermostat shown earlier. That would be a Dometic Single Zone, the same thermostat that controls your fan and cool.
There is a switch on the furnace that is not identified in any literature. In the first link scroll to figure 1, the switch is inside the opening marked "Electrical Connections" if it is not on the fan will not turn on.
You need to read the "operating instructions on page 5 of the following link.
The following link is for the Dometic Single Zone Thermostat, start by pressing the mode switch until the fan LED comes on and press the + or - button until the dislpas says AU. Then press the mode button until the Heat LED comes on, after about one minute the fan should come on.
If you do have the Suburban thermostat which you can see on page 8 Figure 7 item 2, all you need to do is move the selector arm to rhe right to a number higher than the current room temp and wait for the fam to come on.
Since this is the first time the furnace has been used follow the instructions to clear the dust out of it.
The following link is for the thermostat.
Hope I have not confused you too much and HNY