The best way to carry gear on a tour is as follows:

1. Buy a grill such as https://www.amazon.com/Quick-Grill-M...grill+portable . I got a cheap one at a supermarket ( $5 ).
2. Take the top part and put it onto your rack to make a super big rack.
3. Put your rackpack on the grill and use the rest of the grill as framing for sleeping bag, tent, and stuff.
4. Keep it all together with bungee cords.

I never liked panniers they act like a sail with a crosswind. You will minimize drag by piling the stuff behind your back .

Thanks,
Yan