...or, if you can find the parts, you could look for a Kickflix caddy to mount on the seatpost...

...then mount a Tern Kanga Rack on the caddy...

...and then a drybag of your volume choice on the rack, looking something like this...

20L bag pictured here


In the front, mounted on the handlebars, I'd recommend an Ortlieb Ultimate bag, again mounted on a Kickflix caddy (provided with the bag). The Ortlieb Ultimate bag is not cheap, but they are well made & waterproof, and it turns into a neat shoulder bag for when you are walking around town and need to carry some bits. Particularly good as a walk-around bag with a small camera inside.



The Klickfix caddy and bag/rack mounts are solid, withstanding the roughest of shakes and shudders, yet easy to mount and dismount. Recommended.