I agree with vents closed with a gas MH, but maybe not with a DP. I rarely have to run my generator/roof ACs as my dash AC will do the job up to about 95 outside. It is recycling/cooling the air from under the dash, not from the ceiling like a roof AC. I leave the vents open in the back of our DP to help get the engine heat out with a small window open on the shady side.
If I think it will get hot enough out I'll turn the front AC to on so all I have to do is crank the generator with the dash switch for additional AC. Usually it's not long enough to bother closing the roof vents.
If I am stopping at a CG when it's still really hot out I'll have the DW turn on another one/two roof ACs and try and cool most of the coach down before hooking to shore power.
