Travel backpack

The GG Crown2 is not frameless, so you might have difficulty storing it in a pannier.  I’m not as familiar with frameless packs as many others here, so they should weigh in.  I think some of those larger volume packs might have removable framesheets, which might be interesting.  Good luck

How about the Mariposa?

You can remove the frame.

There is an easy way to travel with a regular pack if you have a rear rack

http://www.pathlesspedaled.com/2011/07/21/video-backpacks-on-bromptons/

I actually already have an Osprey climbing pack strapped on the rear rack but its frame is bulky and missing a few features I like for hiking. I would prefer to keep the pack in a dry bag. Mariposa/Gorilla was another option, any ideas on how small it could pack? I think the frame is a metal wire so that would be fine to keep on the rear rack.