Hi Joe, I have run our genny while driving to power the roof AC on manual. Don't know why you would want it on auto other than to have it auto start when the temp gets to warm in the coach. When we ran the genny going down the road, we would run the front AC with all the vents closed except the 2 ceiling vents closest to the cockpit. I have read where some turn on the rear AC to keep the noise farther away. Both are ducted units and by closing all the ceiling vents except the front 2, forces all the air up front.
About the genny running constantly while driving............only if you need to supply power your AC or other needs.
Our temps on the return trip were in the low 80s, we did not have the sun coming directly through the windshield and we were able to stay very comfortable all day.
We did a cheap fix for the sunvisor for now.
Hope this helps,
Darrell