I believe you are doing great as always.
Rene, Followings your CCIE R&S labs and visited many other online sources claiming that GNS3’s IOU feature does support 95% of the switching incl L2 - L3.
And I have personally checked this feature and assures that it does support switching as claimed by many. However, while creating Q-in-Q tunneling lab, following your demo, I was although able to run all the required commands on the switches, but upon completing the lab connectivity & configs, I was unable to establish connectivity within the two routers.
For your ref, I am attaching the config & topology file. Kindly review it, if you could find something missing in it.
SW1.txt (1.3 KB)
SW2.txt (1.3 KB)
SW3.txt (1.3 KB)