Update: I haven't been able to find panniers that fit the RadExpand 5's rear rack, but this REI "Beyonder" trunk pack attaches securely, is easily removed for carrying, and is large enough to hold 1 bag of groceries (and carry a knapsack while en route to the store). Inexpensive too--less than $30--so this'll be my cargo solution for now: https://bit.ly/45Qnhcz

RPB staff sold me a Fremont pannier, but I quickly discovered the attachments won't allow it to be mounted far enough back on the rear rack to prevent heel strikes, nor does the bottom clip adjust to a position where it can be attached. The RPB staff at my local shop claimed to not have been aware of this. For grocery runs, I'd really like to have a couple of easily-removed panniers on the back of the bike, rather than attaching a basket or (for my needs) a too-small trunk pack. Have any other Expand 5 owners encountered this problem? Are there other brands or hacks that would work? My Ortlieb Backpackers are too large.