A quick look at the
http://ortliebusa.com/product/saddle-bag/ I am not sure how long these have been on the market but I wish I found them sooner. The bags are lightweight tough waterproof and sell at a fair price for the quality. I bought mine here
https://www.biketiresdirect.com/product/ortlieb-saddle-bag at a great price using my accumulated bonus points.
Loaded it up hit the pedals and everything functioned perfectly. I normally don't travel with my ipad mini but it fit inside with many other items. It's Huge! Comes in smaller sizes too. The bag can accommodate a diverse range of packing from light to fully loaded. Layers,food,water etc.
The mounting system is securely attached to the seat rails and you press a button to slide it on and off. A velcro strap snugs it up against the seat post. I like being able to quickly dismount the bag enabling me to take it inside a store,rest area or in and out of a vehicle.
I found it easiest to pack with it on the bike. Having a clean top tube is nice for keeping phone and snack distractions to a minimum also easier access to H2o bottles.
Waterproof has a roll closure and 3m reflective scotch lite. A plastic stiffener inside maintains shape.
Cargo was securely held in place over hill and dale. A quality German product.
Solid mounting no wiggle experienced and I had it loaded to the gills. I give it the Alexander Supertramp award!
