Loading chunks of tiles during runtime

Godot Version

4.1.3

Question

I’m making a game where the player will be able to place ‘chunks’ of tiles, which is a premade 7x7 block of tiles. My problem is that I do not know how to store these tiles. I intend to have several dozens, but I do not know the best way to go about this. The best solution I can come up with right now is putting them all on a single tilemap and copying portions of the tilemap, but this seems very inefficient. Is there a certain node/nodes I can store them in?
Whatever system developers used for games like The Binding of Isaac’s rooms should work here. I need groups of tiles to be picked at random during runtime.
New to Godot, so I might’ve missed something obvious.

In the tileset editor is an option to have patterns, which you can also access in code with get_pattern() and set_pattern(). Have a look at this, maybe this if what you are looking for