Arkel Dry lite
Going back to the Arkel Dry Lites. I am reading that a main concern is the pannier staying attached to the rack on rough roads. My Arkels have hooks on the bottom of the panniers and also velcro straps fastening them to the racks. As a security measure, I also use a zip tie through the D rings on the top of the panniers. This would be extra insurance on the panniers not coming off, although I never felt the slightest concern about this.
You mention riding tandem. Capacity could be an issue. Roll top panniers (such as the Dry Lites) are more forgiving when you try and stuff them full after a grocery run, etc.
You might also consider the lightweight Rockgeist Microwave pannier. They would be especially helpful if you are a tent camper. you can remove the stuff sack of gear quickly, leaving the 'holster' on the bike.