I see what appear to be ventilation holes in the top of the Rio Car. The installation in one of my vehicles will require mounting it underdash, so the top of the unit will be right up against the bottom of the dash (and not far from a heater hose, so that section of the dash will be quite warm to the touch although not burning hot). There is no mention in the manual about leaving those ventilation holes clear (as I think there should be if this were neccessary). Is this an oversight, or is ventilation in fact not neccessary? Is there any reason to be concerned that such an installation will compromise the lifespan or performance of the unit?