snowdance,
Your idea has some merit, but there can be a catch. Running with a window or vent open in the rig creates a low pressure area inside. If the water splashes out of the p-traps in the sinks while you're trucking down the road, this low pressure can cause the gray tank odors to be drawn into the rig via the air admittance valves in the plumbinb. And trust me, the gray tank can smell just as bad as the black thank! LOL :) Now if your rig doesn't use the air admittance valve(s), then there's no problem with your method.
In a longer motorhome, though, the lowly chassis A/C won't be able to keep up in hot weather regardless.
~Rick
