If the fridges condenser coils are on the back, why not leave the vent (or at least some of it) intact to allow the heat from the coils to be dissipated outside the RV? Remember that the fridge is nothing more than a heat pump, moving heat from its inside to the outside; it seems to me you'd ideally like that heat not in the RV, at least during the summer. (It also would be more efficient if there wasn't too much heat buildup around the condenser coils.)