I demonstrated this live during a Creating Star Trails Webinar. Here I am going through all of the steps including some advanced masking techniques.
The total time is about 12 minutes. See if you can spot my several faux pas (there are a few)!
Hint: I seem to be hunting to find the "Duplicate Layer" option. And I did something wrong regarding the watermark... did you spot it?
The AdvancedStackerPlus (advancedstackerplus.com) was released in October, 2013.
A newer version (14E) was released on June 30, 2014. Operation is nearly identical except we removed many of the annoying pop-ups from the Do This First.