Combustion products probably rise in confined spaces (i.e. smokestacks) .... where the combustion debris heats up the air molecules around it and then the air rises - carrying the combustion products up with it fairly rapidly within the confines of the vertical exhaust smokestack.
This is not going to happen anywhere near as pronounced, if at all, out in the open (i.e. right at/after the end of the generator's horizontal exhaust pipe) where the hugh volume of outside air down low all around the RV and the exhaust pipe will immediately start cooling the generator's combustion products such that much less "rise" of anything occurs. The fumes remain fairly low in the area around the RV.
I've proved the above over and over again in with our motorhome. An open dinette window right above the running Onan's exhaust pipe indeed does soon bring inside a slight exhaust smell of course - due to some small amount of wind and/or a small amount of slightly warmed rising air caring some fumes. When we then change over to our coach pressurization technique (with the generator still running), all fume odors in the coach vanish within seconds.
When going down dusty roads not immediately behind another vehicle, all dust from our tires stays down low enough such that our coach pressuriztion technique keeps the interior free of dust even though a roof vent is open way up high with the fan (slightly) sucking in air to maintain the interior pressure .... thus preventing the dust from entering anywhere down low.
To the OP: I apologize for the diversion from you inquiry. We do use a PSW inverter in our rig to supply small levels of power for all sorts of things .... including a non-heating CPAP device each night. Large inverters should indeed be mounted close to AGM batteries to minimize voltage sag between the battery terminals and the inverter input when high currents are flowing. AGM batteries, especially, have very low internal resistance and hence can supply instantaneous large currents that can cause momentary high amounts of voltage sag that will trip inverters. (My diversion, in defense of selected use of RV generators in addition to any inverters on board, merely got out of hand!)
