Thanks for that. I shall have a look at it. The appendices sound the interesting bit.
I have always felt people are careless with median stacking. Transparency changes can have a huge impact on the results – simply normalising the backgrounds isnt enough, normalisation of the signal received is necessary too if you want to do things thoroughly (so some sort of gain correction is necessary). I tend to avoid really long exposures and median stack images in sets of ~10 and then coadd all the resulting frames.