Thanks for that Garfield,
I'v not heard of that one previously. The fumes from the paint would have to be very concentrated (>5%of the air )to radically affect an LPG flame. In this case I think its unlikely to be the cause as the fridge flame draws it combustion air from outside the caravan.
250Bob
I'v just re-read your initial post, and realised that you weren't referring to the gas bottles, sorry for that. However you may have an issue with the fridge.
All the installation instructions I have seen for the Eletrolux fridges (Now Dometic) require the fitter to produce a 'room-seal' around the sides of the fridge. This is to limit the transmission of flue products from the burner to the inside of the caravan. If the seal were adequate, then you should not get any smell from the burner inside the caravan.
Don't get the idea that you have a dangerous situation, in reality the size of the flame in a fridge is very small, not much bigger than a pilot light and much smaller than the open flame on your cooker hob or oven, so the amount of fumes they can produce is quite limited. It would only be a problem if the caravan were completely sealed, with no ventilation. However the fridge should be better sealed than it is.
The smell of the mercaptans (the stenching agent, would normally be burnt off in the flame, but as the pressure in the gas bottle drops the mercaptans can become slightly more volatile and emerge in a grater proportion than normal.
Incidentally in case you didn't know, LPG (liquefied Petroleum gas) in the common butane and propane forms actually has no smell, so to make it noticeable the companies dose it with a stenching agent.
I still think a service may be a good idea.