We have been in a dry dusty campsite for 9 weeks and I wondered if it would be OK to hose the canvas to get rid of the dust or is there another way to do it?

As long as you brush with a soft brush first but don't use a high pressure hose, it should be OK, the water should bead on the canvas, if it doesn't and you feel any dampness inside afterwards it means you probably need to reproof the canvas which is called Sunbrella
https://www.polishedbliss.co.uk/collecti...03-fabric-guard https://sailrite.wordpress.com/2016/03/1...brella-fabrics/
Dave

Absolutely do not wet it before having dusted it. You can use a brush or, better still, an electric or battery-powered vacuum cleaner. If you don't have it, it will come in handy for a thousand other cleanings.

The poptop is made from Sunbrella canvas, below is the recommended way to clean it.

https://global.sunbrella.com/en-us/how-t...a-marine-canvas