[Jamesp]

Total time spent was about 12 hours over about a week. I do clean everything and repaint etc. as needed so it looks new.

I used a standard 120 volt vacuum pump made for AC work. They are inexpensive and effective, pays for itself in one job. I've tried other tools to pull the vacuum and failed miserably.

I did use the exact same foam as Meir, its available at Home Depot in the heating and AC department. It appears to be a higher quality foam than OEM.

If you have foam coming out the vents, it wont be long until the AC starts mixing with the heat, and due to the way the heater box is constructed the air won't be forced through the heater core, a half to a third likely meanders through whether heat or AC is selected.

I think you can do a reasonable job on the bigger of the 2 doors which is the AC/Heat selector by simply taking out the heater core and closing out the holes on the door with foam or aluminum tape. To get to the entire door surface it may need to be moved by selecting heat to tape part of it, then select cool to rotate it to reach the other part. If somebody tries this, please post. I only thought of it after becoming familiar with the heater box geometry.

The door that cannot be reached from the heater core location controls air going to the dash vents so you can just manually close those if you try the simpler fix listed above.