Sometimes you want to put the whole canvas into washer, is that okay?
It is possible, but make sure the temperature not higher than 65F, and soap have to be mild, or it will hurt the canvas coating badly.
Normally, 2 step can make the work completely clean.
1, Remove the canvas from Roof top Tent.
You can find zip inside the tent, under the shell, between shell and the sleeping board.
2, Power wash The canvas, canvas could be on your drive way.
3, Air try it completely, and then put it back.