Yeppers,

I use a nelson longflap, My frame is pretty small surly XC 50.

I use the saddle bag with a blackburn rack and I made a quick release for the bag.

One mis conception on the saddle bags is that you dont need support.

In europe folks who use the larger saddle bags use a support of some type so they wont hang too low.

as for your sqr bag I believe they include a support and the seatpost quick release.

"John"