Yukon in September -- how late is too late for safe travel?

Joe's story reminded me of camping in Alberta (near Drumheller) and having to use a huge mosquito net draped around my entire body like a big tent just to use the port-a-potty (car camping, so no real shelter). I once tried camping on a back road in the middle of some canola fields out there and gave up when I saw a huge swarm coming my way. That will put you in high gear, for sure.