No experience but have heard many positive stories, and yes the carafans are bloody expensive. If you think about it and compare what the little scupper vents do, and they are not bad, and help, the Dometic system is just a "very large scupper" vent with a filter. Like with a scupper vent, the more pressure, or speed, the more air that gets forced in the better it will work. Hopefully someone with one, who has done a good selection of dirt and corrigation, will get back to you. There are dirt roads, and then, THERE ARE DIRT ROADS......
The Dometic DRS works well as similar to a large version of a scupper vent. Some of the positives are that it has a filter, does not have to shut off in the event of rain and is straight forward to install. It will not be as efficient as a Carafan, however it does work well, we have travelled the Onnadatta Track and very little dust has entered the van. Obviously if you travel close to a vehicle ahead raising a lot of dust a Carafan would be better. Whatever you install make sure your fridge is totally sealed to the outside venting.
Hope this helps.
