I'm watching this thread with interest. I still haven't got the hang of >3sec flats with my lightbox and CCD. Have been meaning to shoot skyflats, but so hard to get out that time of day with a young family.
Lately I've tended to just use Dynamic Background Extract in Pixinsight when I'm being particularly lazy. I knew I was in trouble when shots I took at Wiruna with very dark sky came out better without flats than corrected...
