I've got a Nelson longflap that I use to commute with. I'm using the Carradice Bagman QR bracket (without a support frame) and a rear reflector bracket I had lying around as a stand-off to keep it away from the seatpost.
Works really well, though I've made an internal frame out of some dowel to help the bag keep its shape.
Works really well, though I've made an internal frame out of some dowel to help the bag keep its shape.