I think it is ridiculous these things have such dirty exhaust in 2015. This is my number one pet peeve with RV technology. The least suitable to purpose system in the RV-dirty exhaust a few feet from a living space. The clean up using today's technology would be trivial.
There's not much you can do about it. You might make them more environmentally friendly with less particulate emissions, but at the end of the day you are burning gasoline and you are going to have carbon monoxide.
Dirty or not, it will kill you dead.
Everyone ought to have CO and propane detectors in their RVs.