I use the Camper Longflap, and find it just right for carrying, tent, bag, mat, cook set and clothes in the main compartment. If you are worried about space between the bag and the rear wheel look at the Bagman support. I have to use that support if I put the Camper on my Ramouillet, but I don't need it when I use the Cervelo RS. One advantage of using a relaxed geometry modern bike over a classic sport tourer geometry is you end up with lots of room between the saddle and the rear wheel.

Definitely get a bag with a longflap and it give you options to carry stuff like bulky food. You can also strap stuff to the top of the bag using the metal rings on the top.