The coal being burned can be one of the biggest variables in the amount of fly ash. The deep mined coal I purchased this year allows me to empty the ash pan only every 2.5 days instead of every day , however I have noticed that I am cleaning up fly ash on a more regualr basis.
Besides vacuuming the stove every week I have been running the SWG at full speed and holding the baro shut while tapping on the flue to loosen up the ash. Much of it flies right out the vent (both my stoves use a SWG power vent). You need to lubricate the motor with the SWG super lube every 3 months as well as blow out the ash from around the cooling fan on the motor. After that a quick shot of WD 40 or similar on the cooling fan keeps it from getting corroded. I know of folks who have had to replace the motor assembly in less than 2 years on a SWG just from corrosion caused by the fly ash in the little aluminum cooling fan on the motor assembly.