Don,
That's outstanding outside-the-coach-box thinking! Using OEM capabilites in your RV over and above their obvious purpose is definitely beyond the norm. ;)
BTW #1: That approach will of course also work for hot weather air conditioning when going down the road.
BTW #2: While doing both of those winter and summer things you can also keep the dash heat (winter) and dash A/C (summer) on it's recirculate setting so as to not have outside air continually dusting up the hard-to-clean coach interior.
BTW #3: In the summer we always use our dash A/C with it's air flow set to Defrost so as to gently bathe the interior with it's chilled air instead of having uncomfortable chilled air blasting our face and arms. With the dash A/C air flow set to recirculate, you also get the chilled air coming out the floor outlets (in the Ford chassis) to cool the hot cab floor. Some folks may not realize that the (Ford) cab A/C can be used in this windshield/floor split air flow way for better distribution of cool air.