I often had a very faint smell in my camper. It wasn't there all the time and for the longest time I just couldn't seem to track it down. Seemed to be coming from the sink, but not quite.
I also noticed that it took a long time to get the burners on my stove to light. One day I lifted the top of the stove to clean under it and discovered the smell was because the regulator for the stove (that is mounted under the burner cover) was bad. It was bleeding a very small amount of propane out of the seal.
I ordered and installed a new one, no more smell and now the burners light right away.