Bend a nurbs cureve ento the entire sequence and then animate two trimcurves moovinga along the curve! trim at both ends (leave a bit room for those trims, as the point at hwre you click for the trim is important to lie on the side you either want to dlete or keep. In this case you must use 2 deletes)
OR bend the same curve (this is to avoid flipping, but gives you also controll over looping etc.) add a curve on surface in the middle. Then attach a nurbs plane to the animation curve (use normal as up), and do a oath flow with local settings.
if you need some undulation slightly animate the points moving during tha animation.
