Running generator while driving in the rain

I just downloaded and looked through the Onan Diesel Generator owners manual. I don't see anything in the manual that talks about operating in the rain. What I did find is that the air intake for both the air into the air filter, and the air for cooling the engine come in from the bottom at the front. This is the same generator I have in my motorhome so the air intake going into the generator engine is just behind the front bumper of my motorhome. So it is very likely that in the rain water could be splashed up into the air filter if the motorhome was driving down the road, but not while the motorhome was stopped. Will that hurt anything? I have no idea. But you would have to ask why put the air intake on the bottom? Why not on the sides or on the top? Could it be that the designer of the generator wanted to make sure that no matter how the generator was installed in whatever vehicle it was to be used in, that the air intake would be on the bottom so rain wouldn't get into it? Seems to me like that would be the main reason to put it on the bottom to make sure it was waterproof.