Hi Skipworth,
I managed to read through the years 1798-1800 of the Manchester Mercury. There was some coverage of Stockport but I didn't spot anything about a fire.
I'm going to read through a couple of later years next time, because apart from anything else, I was totally fascinated by some of the stories in this newpaper and the way they were reported,who knows perhaps something will turn up for your William. I'll let you know if I come across anything.
Regards,
Pat.