Troubles making a GUI accessed from a keybind

I want the player to have a GUI that they access by pressing a button and use it for a custom crafting function. I've developed a similar system using a block and it works as intended. However, since this GUI isn't tied to a block, I can't use the normal block inventory procedures. I'm trying to use the GUI procedures and tie them to a non-inherited inventory, but I can't seem to get them to work. Is it possible to make a GUI like this?