My workshop has so much stuff in it I decided to forgo the attempt at eliminating sources of dust. While the varnish was wet I took care not disturb anything that might generate dust. I believe that worked well.
i forgot to mention the other thing I learned while varnishing. The hymnal suggests (IIRC) sanding with 320 grit between varnish coats and then wet sanding by hand with 400 before the finish coat. Long story short, after some experimentation I decided to use the scotch pads that the materials list suggested buying. It did a great job of knocking down the tiny bumps left after varnishing, that the tipping is supposed to knock down but may not have been completely knocked down. Also the scotch pad gives the surface some tooth for the next layer to adhere to.