) I have popped one leader that I can recall, but nothing like your situation. I can say since I've been tying my own tapered leaders from Maxima material, I feel like I could pull down a birch and not worry about the leader breaking. I'll be interested to hear how you like that box, Bob. If my past is any indication, I'll end up with 3-4 of these solutions, this box being one.
The idea of a thick foam door hanger with some slots cut in it sounds good too. Something to try for sure. It would be stiffer than the cardboard and retain the slots better.
On the Smith Creek Rig Keeper, the plastic "walls" or panels are intended to protect dry flies as well as keeping flies from getting brushed off as it rubs against arms or packs. They make a fly patch with similar design. I can see where that might protect flies from getting snagged taking this in or out of the pack. I'd still pop it in a small ziplock to keep it all together.
My concern is tying a rig up too early (a few weeks, or even a week in advance) and having memory set in the tippet as it makes those tight turns on the holder. Even for Tenkara rings that hold a Tenkara leader there are memory issues.
Those of you who use these pre-tied rigs, do you find issues with memory in the tippet? The cards Bill Lovelace showed would help with that.