Congrats on your 'new' camper! Wheres the pictures?
On the heater though I would be surprised if you had a non fan unit-
IF it has a fan thats is not coming on hopefully the burners isn't either as it shouldnt work unless fan is running.
This is our heater
If you have similar ducts or outside cover as shown it has a fan.
Removing the outside cover allows accessing most internals if needed.
Start with simple stuff, check fuse on converter panel. Check the thermostat, jump the terminals bypassing the thermo switch, ours took a few seconds before the fan came on, then several seconds later before heater lit. Remove outside cover ensure the switch (if it has one) is on and the thermal breaker isn't tripped.
Assume you don't have the paper work for heater-record any/all info from tags, primarily model. Most Atwood heaters online manuals can be downloaded. Relatively easy to trouble shoot if comfortable with it.
My assumption unless p/o said it hadn't worked in years, if its been setting /dirty.
Awaiting pictures...