Back on page 1 I offered this comment about the Ortlieb Trunk Bag under review:
"Second, on a single rail rack like the Vega, you can't use it in combination with Ortlieb panniers. That's because the clever mount dominates the rail. Traditional saddlebags don't display this incompatibility. (You can use it with panniers on a dual-rail rack such as the Tubus Logo.)"
Well I can tell you now that the remark in parentheses is inaccurate. I have purchased a Logo Evo, and it certainly will not mount the Trunk Bag with an early pair of Back Rollers. Yes the top rails are free. No, they are too close to the lower rails, and the Trunk Bag is too wide, to prevent interference. I'll edit p1 accordingly.
I had other reasons for getting the Logo rack, so that's not a major setback.
Photos are of a Logo EVO, Ortlieb Backrollers from about 2010 vintage, and the Ortlieb 31 liter Ortlieb RackPac of similar vintage. The Rackpack is up above the rack, it sits on the Backrollers, not on the rack.
This is the USA website for Ortlieb Rack Pack
https://www.ortlieb.com/usa_en/rack-packThe Rack Pack has a strap on each side that clips to hold the rolled part down to the rest of the bag. And the Backrollers have a strap that goes over the top of the pannier. You can use the Backroller strap to clip to the Ortlieb top clip on each side to hold the Rack Pack.
First photo from behind. Sometimes I add one more strap around the rack and Rack Pack, did that in the first photo. That helps keep the Rack Pack from sliding around and shifting position.
Third photo, the Rack Pack shifted to the left side away from the camera, it is in part a function of how tight you have the straps.
The Rack Pack is basically a duffle with minimal stiffener. There are stiffeners at the roll top to aid in rolling it, but that is all. I have commented earlier in this thread that I have used initially paper based cardboard and later Coroplast as a stiffener in some of my bags. I did that with the Rack Pack, thus the Rack Pack has a firm cylindrical shape (or maybe flattened cylindrical shape if not stuffed full) instead of a limp pillow case sort of shape.
Since the Rack Pack sits on the panniers and not on the rack, it will not work on a rack without panniers. And it is best if the two panniers are the same height, or equally loaded. And it is pretty obvious that the Rack Pack goes on last and comes off first.
If I did not want to carry that large a volume, I might leave the Rack Pack at home. Ortliebs are expensive, instead of buying a smaller one, I use a non-cycling dry bag on some trips instead. Fourth photo. This obviously was not designed to work with the Ortlieb straps, so this is more complicated to attach and detach. On this trip by the end of the trip when the food was all eaten, I all gear was in the panniers and handlebar bag, no bag on top of the rear rack.
It was not until I looked at the video in the Ortlieb website for writing this post:
https://www.youtube.com/watch?v=OtxsoOa2h48that I realized that I was not using as many of the straps as I could, thus the Rack Pack might not shift side to side if you clip all four clips where I was only clipping two buckles. I just learned something.