Here is an exercise for you.. If you have a FORD chassis, go find a Ford F-350 Custom Straight truck.. Take a look at the cab of that truck.
If you have an "Other than ford" Find a truck of simular size and type (Straight truck or Semi Tractor) and take a look at the cab.
THAT. is what the dash air is designed to cool.. That cab.
now, take a look at your big 30+ foot long class A.
No way on earth can it keep that big a house cool (Less of course it's Feburary and you are in Wisconson) but wait.. there's more.
Take a look at the amouont of windshield in your greenhouse v/s that straight truck.. Yup, it gets hot in the cab in Michigan in January due to the effects of the sun too.