I finally found a side case that won't clash with the aesthetics of the CE-04, and seems to blend in without distracting the eye. Unfortunately, they don't sell them out of Wunderlich America. But, they told me they could order one from their European counterpart for me.
Wunderlich Business Bag
That looks like a slightly enlarged version of their "Business Bag", i.e., hump bag, that I ordered last May from Wunderlich America, while awaiting delivery of my C 400 GT:
The part that puzzles me a bit is the dimensions of the 42011-002 that you're discussing are different from the dimensions of the 42010-200 that I got, yet both are listed as having a capacity of 8.5 L; see
https://www.wunderlich.de/shop/en/wunderlich-business-bag-42011-002.html and
https://www.wunderlich.de/shop/en/wunderlich-business-bag-42010-200.html .
BTW, it's also unclear to me if you get one bag for each side, or just one bag, period. The price is slightly more than double the price of the hump bag, but the listing for the 42011-002 doesn't seem to mention anything about two of them.
(Incidentally, I don't know what the shipping would be if anyone in the USA ordered products from the German site -- if that's even allowed -- but the 42010-200 I got is cheaper over there, at least at current exchange rates. Compare and contrast
https://www.wunderlich.de/shop/en/wunderlich-business-bag-42010-200.html with
https://www.wunderlichamerica.com/BMW_C400_GT_Business_Bag_Tank_Bag_Style .)
In any event, I intend to use the bag for multi-day out-of-town trips, but I haven't done one since getting the bag. (I had cleared my schedule for part of last summer for a ride from NY to NC, to visit a daughter, but rain and her getting covid put a damper on that.)
The bag certainly appears to be well made, and looks like it's rainproof (although I haven't taken a hose to it). I have some pics of the one I got, including some mounted on the C 400 GT, if you're interested, in my gallery, starting with this image and caption:
