Welcome to Sunline Owners Club and congrats on your new to you coach!
On the furnace, here it helps to have make, model and serial number if possible. I may be able to find a manual on line for it for you or we already have one in our files section.
I do not know exactly what the system you have is being that old. I'm assuming you have the stove able to light and the hot water heater? If you have both of them working that means the LP gas system is at least supplying gas to the camper appliance thru the main regulator.
Most of the newer furnaces and many older ones are electronic ignition however that does not mean they all are. I'm "assuming" you are staring at a gas valve that has a gas knob on it that you hold down to allow the pilot to be lit and then the thermocouple warms up and keeps the pilot lit to allow you to release the knob? Yes/No?.
While I have seen many gas heaters like this, I myself have not seen one in a camper so I can't help much without a make,model and serial number to know what it is you have.
If no one responds with an older unit that has one like yours, takes some pic's this weekend as well and post so we can see what it is you have. Make sure to get the gas valve setup.
If this is anything like a standard pilot setup, odds are the gas valve may be plugged not allowing gas to come out or the line feeding the system has a blockage or both.
Making another wild assumption Sunline stilled used Hydroflame back in the early 80's. Here is a trouble shooting manual on the real old Hydroflames units and this booklet has both the direct spark ignition and the piezo snap lighter for the pilot. This may not even be your heater but it was the oldest one I could find that was Hydroflame and a pilot system.
Since your camper is over 30 years old and you do not know it's prior maintenance, having a gas pressure drop leak test done is a good idea. This checks for any leaks, checks that the gas pressure is correct and that the main tank regulator still is working OK. If you have a buddy who is a LP repair guy they can do this for you or an RV repair shop can. One of the concerns is the main gas line is made out of steel normally and not even painted and by now may be a pile of rust under the camper. If you have it checked and all comes out OK, then great. If any of the steel threaded connections look questionable, now is the time to get those areas repaired. The main tank regulator and the stove regulators at times freeze up as well over time as they are not the highest quality to begin with. Just a friendly heads up to have the LP system checked and if all comes up fine, then go have fun camping.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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