I use the Carradice Camper Longflap (23L) for all my touring and the Barley for day and overnight CC trips.
I don't use a support as I have sufficient clearance between the saddle and back tire. I just strap the bag onto my Brooks Swift and around the seat post. This is how Carradice saddlebags were originally designed to be used.

Dirt is an issue, particularly in the rain and I often get a nice stripe down the top of the bag when I'm on a fire trail or limestone.

I use mine to carry all my camping gear and clothes and the side pockets are great for spare tires, tools and first aid kit. I also sewed on a couple of D rings so I can attach a shoulder strap, but I find myself mostly just using the nylon straps that I have attached to the top flap as a handle.

With the Longflap you can carry an extra 10L of volume and jackets can be easily strapped to the top flap too. It's very versatile and can fit on a plane or train as hand luggage.

Here is my packing list for the Camper Longflap and a picture of my Carradice on my bike. You can see my grey jacket strapped to the top as it was cold in the morning. It usually gets packed inside the bag.

Riding with a full saddlebag isn't that different from riding the bike without it because the weight is so close to the center of gravity of the bike and I can climb easily out of the saddle. However, if you have to pick the bike up it takes a while to get used to the weight distribution.

https://wheelsofchance.wordpress.com.../25/gear-list/