I tow the bunkhouse camper which is a lot like the aspen, I noticed a little of the exhaust fumes until I added a the factory vented windshield. The airflow with the vents on the windshield open must have changes the air pocket behind it just enough to eliminate the problems.
I do have the factory adjustable side vents also, I notice no difference when they are out to make air go around, or in to direct air on us.
I do have a cooler on the front.