Merry Christmas (again) Keith!
Perhaps your "layoff" on the studio work might be to your advantage. Remember the V cutting tool and PE "rope" (for sealing drywall joints) that I promised you a while back? Well, I still have them sitting a box to send you if your still interested.
As to your duct board sourcing problem, I used an OC product (oddly enough called "Duct Board" that, at least until a couple of months ago) was readily available at my local supplier. The only stuff he had in stock we 1" thick and foil backed but I believe it's also available in 1 1/2" and 2". If you can find my thread, near the end of it, you can see the little "elbows" I made from the stuff for my send/return vents in the control room.
It comes is 4' x 10' lengths and the last time I priced it, it was about $45/sheet (in W. Texas). When I got my original order, it was about $36/sheet so who knows how much it goes for today.
My plenums were made from just the duct board (i.e., no plywood outer shell) and work just great! Of course, they are 24" x 24" by almost 30' long (one each for send and return air). If fact the only "problems" I ended up with in the HVAC system were:
1) The loudest sound in the big room is when the relay in the themostat clicks on and off and...
2) I neglected to see if my natural gas line in the building was actually connected to something outside the building. When they came to pressure check it before putting on a meter, it turns out you can pretty much just blow into the pipe. The gas company figures that the pipe collapsed somewhere under ground (on my side of the meter) and that more than likely, when the dentist built his office next to the studio (between me and the meter), it was built directly over my gas line (and was probably severed or capped off) in the process! Since it's illegal (in Texas any way) to build a structure over a functional gas line, they took the easy way out and made it non-functional. I <i>could</i> petition the city to have his building torn down but that would not help much with neighborly relations.
The good side of this is that the rooms are so well insulated, a couple of small oil filled electric heaters I got from Walmart warm the place up from 55 degrees or so to a toasty 72 in 30 minutes or so and then they stay at that temp for a long time.
Anyway, again, a Merry Christmas to you and your family. Sorry, no virtual turkeys this year!
len