Thanks for sending me the link, Keith. I just read through all this.
I need to totally rethink my whole booth plan. I come from industrial fans and blowers, so I was thinking axial fans and small AC ducting for exhaust. It never occured to me to use a shop vac.
And with the very small size of the shop vac plumbing will be much easier to find a way outside. I can't go up through the attic, but I will be able to find a way outside when working with only 1.5" tubing instead of 4" ducting.