George:
Not sure which HO scale dust collectors you were looking at but please take a look at below. I routinely used HO scale parts on my grain elevators. Some samples are shown.
This is Faller Industrial Silo. I makes a pretty good dust collector.
This is a Walthers Cornerstone Surge Bin that I use as a roof top surge/storage bin with piping to two loading bays.
I believe these are O scale - either Rix multiscale roof top vents and cyclones 628-0611 or Bar Mills industrial vents 04024.
Joe