This setup looks really great Dave. I wonder if you know anyone nearby who has the removable SW-Motech racks mounted on an F800GS (see mine below). They leave quite a large gap between the tank and the right pannier, and I'd be eager to see if the Rotopax can, if hanging from your rear plate, might be able to fit in between.
I've got the Touratech plate now, and I've kludged a Rotopax mount to it. But I'd prefer your setup if I could fit a Rotopax down low and behind my Caribou bag.
Oh, and let me add my +1 to Motoriley's "big middle hole for easy plate removal" idea.