They could well be Swiss; I’d googled Danish GA tail markings and found some with the Danish white cross on a red background, summed that to the flat environment and shot from the hip! Had no luck whatsoever finding the airfield, though. A few observations:
A) the loooong taxiway perpendicular to the runway.
B) Denmark isn’t particularly noted for dense forest and, if I’m not mistaken, most of the forested land is in the north.