Unless you are going from extended time running the interstate directly into your site {think KOA's which are almost always located right on the freeway/highway}, there should not be much heat to dissipate. I've never had heat issues with my E-350 V-10 in the last three years and 30,000+ miles. Even when we stop every 2 to 3 hours, often after cruising the interstate, we've yet to have any engine heat problems. Typical average engine temps are 195 to 210 {per the Scan Gauge}.
Our dash AC keeps the cab a very comfortable 72 degrees in almost any weather {therein may lay a solution for some}. As others have noted you can open the hood {never have}, hang a blanket to isolate the cab from the coach, open the cab windows or even let it idle with the cab AC running. Unless you have serious engine cooling issues this thread may be searching for a solution for which there is no known problem {the government does this a lot}. :h
As always.... Opinions and YMMV.
:C