Interesting. The two pushers I've owned blow the air out the back of the RV, not towards the engine and pan. The rad fan sucks air past those items and they usually aren't bothered by dust from the rear tires. If you're going too fast of course, then the front tires will kick up a lot and send it back.
I will say that the possibility of lots of dust being blown around the engine area is certainly high when on a dusty road, but I don't always know when that's going to be true. The last time I was on a country road, it was really dusty. I traveled under 15 MPH, usually under 10. I expected my pushers radiator to be heavily coated after I'd stopped, but when I got the hose out, there wasn't much there. The back of the RV and the rad were pretty clean, hardly any dust visible. But under the hood of the towed car, it was thick. Fine enough that it didn't take much to remove it though.
So I'd say it's a **** shoot. Sometimes on a dusty road it's going to be a mess, other times, not so much.
On reflection, I think the side rads can kick up bunches of dust, if that's what you have...but I have only read about people complaining about it and don't remember if they did anything or not...
