We've had good luck with this case by SKB, part number 3i-2217-8B-C
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.amazon.com/dp/B001Q3KSRU/ref=cm_sw_r_cp_api_okvcybPRG0MY9