Hello Sam
It seems that on GNS3, the particular feature of VTP is something that’s difficult to get working. I have found this very recent post about the topic on the GNS3 forum that may be helpful to you:
https://gns3.com/community/featured/iosvl2-and-vtp-v3
It seems that others have found that the IOSvL2 images don’t run VTP successfully, and only some IOU images work. Specifically, it has been reported that:
For VTPv3, i86bi-linux-l2-ipbasek9-15.1g.bin and i86bi-linux-l2-adventerprisek9-15.1a.bin are fine.
I suggest you check those out to confirm them. If they don’t work, one additional thing you can do is do a packet capture to see if VTP messages are indeed being sent.
Now having said all of this, it has been reported that EVE-NG does support VTP with little hassle. In general, EVE-NG is known to provide Layer 2 support for a wider range of features. It may be worth looking into.
Another alternative is Cisco’s CML or VIRL, which tend to support most such features. More information on these emulators can be found at this NetworkLessons Note.
I hope this has been helpful!
Laz