There should be a connector where RED plastic tubing comes from above the engine, and joins BLACK plastic tubing that disappears into HVAC cabinet. If you run rubber vacuum hose (I got 5/32" but 1/8" might work) from the RED around to inside the van, just through the open passenger side door, TO where I said Cut the Black from the HVAC (rhymes, but I am NOT Dr. Suess...) you should find the controls will work.
THEN, supply vacuum to your new tank from RED through a Check Valve. Then on to inside the van. I'd say get to the passenger side any way you can then fish it between fender and fender liner, to the door post (near the hinges). Forward of the hinge you'll find a large plastic body plug. Take it out, pierce it for the new hose, and push through to the inside. The plastic toe kick trim will have to come off, but that's all. Connect to where you cut. It'll be BLACK tubing coming down from the top of the instrument panel.
I like where I put Acme Roadrunner Bomb on Passenger side because:
1. my wife saw the spot and suggested it
2. much shorter hose runs than to, then from, the coolant reserve tank area
But you've got the plan and it'll work. Like me, you found it's not so easy to find even enough space for a little vacuum tank under a Ford Van hood. I was ready to get a hiker's aluminum water bottle, epoxy a nipple into it, and tuck that away someplace. Heck, leave it in the cup holder and tell folks it's reserved for the vehicle. That little hose feeds the refreshment it needs to carry on...