I remember seeing a bag of holding chest mod somewhere and now I can't find it.

It allowed you to save an item in your inventory, and with a spell, transport the item back to a chest in one of your houses.

Anyone remember this?

I don't remember the mod per se, but I just googled "Skyrim mods bag of holding" and a couple of mods popped up, encompassing both Steam and Nexus. You might google that and see if one of those is it.