RJM Music Technology, Inc.

We've had good luck with this case by SKB, part number 3i-2217-8B-C

https://www.sweetwater.com/store/detail/3i22178BC--skb-3i-2217-8b-c-22-inch-by-17-inch-by-8-inch

This case has perforated foam so you can configure it yourself. For a GT/22, tear out everything but 3 squares on each side. For a GT/16, you just leave 9 squares along the bottom. I only needed to remove foam squares from the top layer (there are 3 layers). In the second layer, I opened up a couple areas for an AC adapter and its cable. 

Customers have also recommended these cases for use as pedalboards, so you can mount expression pedals next to the GT:

https://www.thomann.de/fr/thon_customcase_fuer_bodeneffekte_2.htm