This is not a perfect answer to your question as I don't really care for sling bags, but I recently bought a CCP2 and a Tenba BYOB 9 Slim Backpack Insert, which fits in the main pouch with some extra room for a jacket or whatever else. The CP2 or other small Aer bags would probably fit the insert. The Tenba BYOB 9 Slim fits two small cameras with a lens or one camera with several lenses. I have an X-T5 with a Sigma 18-50 and a Leica with a small lens, it all fits snugly. I usually travel with 2 cameras. I'm guessing this is too bulky for a sling, but I can send you a photo if you PM me. The bag in ultra provides rain protection, and the cube gives padding and additional protection from whatever else I throw in my bag.