I may be wrong, but my understanding is that in your circumstances you can't log the flights as one entry as you are going to a different airport.
I always believed this rule was aimed at people doing other activities, such as banner towing, instructing, pleasure flying etc where they operate out and back to the same airport without landing elsewhere hence
returning on each occasion to
the same place of departure
You would then log Off blocks as first departure, On blocks as last arrival and total flight time as the sum of the x sectors you flew.