After the purchase of our Sprinter passenger we realized that it takes quite awhile to cool the rear (no rear a/c) so we are wondering how to solve the problem. I remember seeing a fan on some parts site that you (or a dealer I guess) can install in the celing to circulate the air. Has anyone installed one of these? They are fairly cheap and from what I have read it is not possible to install an a/c roof unit after the fact. Thanks!