It is flat out rude to blow diesel exhaust at anybody. It is extraordinarily obnoxious and it might even be dangerous. There is a story where someone died from CO poisoning at a NASCAR race inside a motorhome. Worse, it makes my wife grumpy when she smells it in her motorhome.
The simple, easy solution is a Genturi. It is well engineered and easy to use. Its one unique feature is that, using a venturi effect, it mixes air with the exhaust so the pipe stays cool to the touch. Not only will it send the stink skyward, it won’t burn anyone that touches the pipe.
I have two. One for the Onan and one for the HydroHot. I’ve used the one on the HydroHot for about 1500 nights in eight years. It works. The one on the Onan is only used when I’m dry camping.
When the coach was new, I went to a lot of rallies where both Onan and AquaHot conducted seminars. Always asked was, “Can I use a Genturi?”. The answer from both companies was always, “Our lawyers won’t let us endorse a product we didn’t design or test ourselves.” When asked, “Have you ever, as a tech rep, seen a problem caused by an exhaust extension device?”, the answer would be “No.”
My installation is a little different. To hook the required support straps to the motorhome I bought nice and pricy stainless eyes and screws from West Marine. I attached them to the “waste band” that functions as a hinge for the basement doors. I did not think it was a good idea to put screws in the sidewall itself. On the HydroHot, the Genturi pipe almost fit directly into the polished exhaust extension. A few minutes with a file and it did fit. With it inserted, I drilled a hole and use ¼ inch bolt as a pin. For the Onan, I used the adapters that come with it.
I think is absolutely necessary to send diesel exhaust skyward. As a hot gas, it will continue rising, but you have to get it started. Any way you do it is good. The Genturi appears to be the best solution you can buy as a kit.