Ned the lp odor seemingly emitting from your duo therm furnace when the container is almost empty is not typically attributed to the furnace itself but rather the level of fuel in the container.
Rv furnace stinks.
It can happen when you have a bad thermostat.
This can be found in any part of the rv but is particularly prevalent in corners under mattresses and in other small nooks and crannies.
This is the ultimate result of other issues that can be with the whole furnace system in your rv.
Dump or spray it over the regulator and look carefully for bubbles.
When i first noticed it last year i nearly went nuts looking for a non existent leak.
It does this whether i m using the frame mounted tank or the 20 lb.
Musty or mildew smell in rv.
A low propane pressure at the furnace ca also result in furnace not lighting.
A small brush and soapy water can be used to check fittings for leaks.
Lastly there s the dreaded musty or mildew smell.
You can test for leaks by using a dish soap water mixture.
This is the smell of a water leak and it likely means water damage as well as the potential of mold.
Propane odor can come from many sources in and around your rv from the propane tanks to the stove oven refrigerator water heater and furnace.
Make sure the thermostat is is fine working condition.
If a propane smell is coming from your rv propane regulator it may be damaged and not sealing properly.
When my rv s propane tank is nearing empty i get a strong propane smell from the furnaces.
Don t forget all the gas lines connecting these appliances to the tank as well.