Whatever you choose it needs to breathe - sealing your OTA in an airtight coffin is a surefire way to grow fungus on your optics.
I had a canvas bag made for the Santel (OTA diameter 260 x 800 long with focuser). Not unreasonable.
But i found something better by accident - we had a mountainBuggy stroller and the padded airline travel bag for this. It turns out this will accommodate an OTA upto a C11. Basically: lay it out flat, place OTA on that, the sides wrap around held with Velcro, then fold the ends over (more Velcro) and do up the outer straps. These bags cost $100 and are padded with a very tough outer surface, and loops for carry straps. The Velcro straps are enough to support at car.
Stroller has gone now and the bag repurposed
Canvas bag is now surplus, if interested.