How can I create a secure Custom GPT for a client?

While I understand your concern, I haven't encountered the "erosion" issue you mentioned in my experience. As long as we keep uploading files and instructions correctly, it shouldn't forget its training info. But I'd love to hear alternative suggestions you might have!

Honestly, I'd advise against doing it. Custom GPTs can lose effectiveness over time, and you don't want the burden of maintaining one. What happens if it no longer meets their needs? It's better to steer clear of that responsibility.

One option is to have your client create their own account and manage payments for you as their consultant. This way, you guide them through the setup without taking on all the responsibilities yourself.