Grease Pencil generates many layers during any composition, and such needs organization and neatness in the forms of groups that can open and close themselves for maximum efficiency of your workflow.

Hence, this addon tackles exactly that, following the same principle of shape key folder management in Shape Key Collections, here the core principle is folder management for all the layers in Grease Pencil.

Just create a folder, select your layer and specify its location. Create your background layers that need not be touched at all after that and just collapse them. Now just organize it all and enjoy the new neatness that this provides.

Shape Key Collections - allows for a folder structure for shape key management - https://blendermarket.com/products/shape-key-collections

Vertex Group Collections - allows for a folder structure for vertex group management - https://blendermarket.com/products/vertex-group-collections