I agree with the others, use a gas leak solution in place of the match method.
Now past this to your problem.
If many years have gone by, dust may accumulate in the heat chamber and it can smell after the first fired up and sometimes a few others but should get less each time.
Since you have an 1985 model there is a possibility of a rusted pin hole or 2 in the heat chamber. This could allow a wiff of propane to come into the camper before the main burner lights. Or that a gasket where the burner attached has a void in it. If either of these are the cases, they really need to be corrected as fumes can then come into the camper as well.
There is another areas that can create a LP smell inside the camper that is not a pipe connection, the stove if you have one has a separate regulator on it. It takes 11" WC down to 10" WC gas pressure. The regulator can have a leak inside the regulator that comes out the vent port of the regulator.
See here where a real fine leak was one one of mine.
I use this solution to check for leaks, it works better than the soap water. You can find it at Lowes/Home Depot.
If you have not had a LP pressure drop test done in a while, this would be a good time to check it out. Here is a thread which may be helpfull
The main pressure drop test will look for fine leaks, including the appliance shutoff valves themselves. If you fail a pressure drop test there is a leak somewhere. It then becomes a hunt on where.
If you suspect the furnace may have a rusted pin hole, if you find a LP service guy who even works on home gas equipment they have a very high end sniffer that can find these really fine leaks. He may also be able to tell you carbon monoxide is coming through and if it is, then you have a leak in the heat chamber or chamber gasket and that really needs fixing before using the unit.
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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