Peak Design 20l with add on hip belt.
There is a TRICK. You reconfigure the bag inserts for two vertical sides and a top shelf.
You can put the 100-400 one one side and the 24-120 plus others on the other side and still have the top shelf.
What's good about it - dual side sling access. This is HUGE for me. You can access both sides as if it were a sling.
Hip belt makes it easy to wear all day but also can be tucked away.
Two side storage compartments.
Top shelf inside can be used for other things you take out that day - phone battery, rain coat etc. I have done many trips this way.
Seems like a nice bag, if a little pricey. So the 20L is sufficient for the 100-400? The bag is wide enough to hold it? How comfortable is it if you wear it walking around all day? The straps seem a little narrow with little padding.
I have had no problem carrying this all day on three week trips. The hip belt helps.
Here you see the what I mean by the set up.
This is a Z6iii with 24-120 and 26 in the red bag and battery charger. On the left you see what I mean is the top shelf.
Here is the 100-400 by itself.
If you want the camera on it, you shorten the shelf making the one side longer.. Sorry quick snap with a phone, it fits fine. From these images you can see once you sling a side you have full access.
Here is the other side with the Plena. Top shelf is on the left here. Grey bag has batteries.
While expensive, built well and lifetime guarantee. I am happy with their products and service. There are ways to interlock the zippers to make them more access proof.
As mentioned the fact that it slings is huge for me for travel photography.