…. on the sides, not the top of the pannier rack
if so how do you secure them to the pannier rack?

Monday bump

I have never tried it to be honest, prefer a framebag, handlebar harness, seat pack set up.

These would be your best bet so you could strap them on to the pannier rack using the loops.

http://www.alpkit.com/shop/cart.php?target=product&product_id=16469&category_id=295

Good luck in buying any, the most usable size 13l is out of stock until further notice.

i use them on top of the rack (ortleib panniers on the sides). just use a bungee or 2 to attach

Erm….why would you? Becuase they are cheap?

But no stiffening and nothing to attach them to the pannier?

Sorry, daft idea, buy painniers.