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.
If I could find a right sized heat shielded catalytic converter I'd give it a try-get it close to engine where it heats quickly. The altitude adjustment screw allows some mixture adjustment (doubt it would take much adjustment-just slightly leaner than stock). Especially at a light to moderate load I bet it could be cleaned up nicely. At a heavy load it may need enrichment (as modern car engines do when they go open loop). Heck it may reduce the useful life a bit- but probably not much if you don't lean it out under heavy load. It may be lean enough in stock configuration anyway..