Lowering a pop-up TC....is there some trick to this?

Boy unless you can really secure the top to keep it from coming down don't place your fingers in to tuck the canvas. Otherwise you might end up a couple of fingers shy of a full set if the top came down on its own. I would be using a push stick if you have to tuck the canvas from the outside at least if the top came crashing down it is just a stick in there and not body parts.