I've been using a Classic rack, with a barley (Super C Audax) for a few years. Needs Brooks saddle or compatible saddlebag loops though... Tabs into saddlebag loops & one strap. Super convenient to swap between bikes, or just get on and off. I tie bits of inner tube (to rack) where the rack contacts/rests on the saddle rails. A bit heavier than my other option, the Ortlieb large roll-end bag, but currently using the classic rack/carradice all the time.
(https://live.staticflickr.com/65535/49509558276_e0e6efa344.jpg) (https://flic.kr/p/2iqZqMJ)IMG_20190330_143508417_HDR (https://flic.kr/p/2iqZqMJ) by ao (https://www.flickr.com/photos/145942400@N06/), on Flickr
(https://live.staticflickr.com/65535/49509788882_0a37365e74.jpg) (https://flic.kr/p/2ir1BkG)IMG_20190330_143516849 (https://flic.kr/p/2ir1BkG) by ao (https://www.flickr.com/photos/145942400@N06/), on Flickr
On diff bike...
(https://live.staticflickr.com/65535/49509590846_08e27f5872.jpg) (https://flic.kr/p/2iqZAth)IMG_20190901_085407912 (https://flic.kr/p/2iqZAth) by ao (https://www.flickr.com/photos/145942400@N06/), on Flickr