[JLMounce]

Your profile states you're in the DFW area, so this may not be a concern, but you need to watch out with vacuum pumps anywhere near high altitude. If you do, or plan to take the car to somewhere like Colorado, you can damage the vacuum pump. Most of them are set on a static switch typically to provide around 18" of vacuum. They'll never reach that at higher altitudes where barometric pressure is lower, so they run constantly and burn up.

I would think that the vacuum canister alone should be all that is necessary as it will store the highest vacuum received, which is typically during light cruise. How much vacuum do you see in that driving situation? I'm not well versed on how much vacuum the diaphragms require to operate correctly, but I wouldn't think you'd need 18+ inches of Hg. Maybe I'm wrong? Is it possible the hvac door and hinge mechanisms need lubricated to make it easier for the diaphragms to work optimally?