Called Bruce's last week with the same question. They said a hose, some light detergent like woolite, and a soft bristle brush. Hang dry out of the sun.
seems the general consensus, and I agree, is that machine washing really reduces the lifespan, and water repellency.
beats the fabric to heck just to clean a few spots.
I agree that when a lot of dust and grit stick to the fuzzy soft side, you don't want that against your canopy, but if it's not moving, then the chance of damage is minimal.