There is an easy way to put an animated GIF onto another animated GIF.
I used 'Will's Scrip Pack' from here:
http://registry.gimp.org/node/24408Quick Howto
A made the background GIF from a time-lapsed clip of an aurora (aurora australis).
I made the second half of the frames series a backwards copy of the first half of the frame series so the
aurora doesn't stop somewhere and jerk back to the first frame. I have called this the GIF 'infinite mode'.
I positioned the top GIF on a transparent canvas the same size as the background GIF.
Both images have the same number of frames.
Then I opened 'Will's Script Pack' Animation Merge.
This scrip makes it stupidly easy to merge the GIFs into one.
Here's the settings I used.
As usual the GIF quality is rubbish but a better animation is here:
http://i.imgur.com/lwyyI7a.gifvI'm sure the Animation Merge script could handle adding GIFs to previously merged GIFs.