Blackburn developed thr Outpost Elite Universal Seat Pack (USP) to work with dropper or standard seatposts, be able to carry a bevy of cargo, and be stable enough to not swing around while it does.
The USP is a two-part system: Part 1 is a T6061 Alloy Wing that affixes to your saddle and works with a standard or dropper post. Part 2 is a removable and waterproof dry bag. The bag has a scuba-style air bleed valve to assist with compression while off the bike. The wing stays on the bike, the bag comes off and allows you to pack, compress and go ride in the snap of a few buckles.
B-Stock - This product has one or more B-Stock units available. These units can be purchased at a discount (see option select). B-Stock units were returned from other customers and may have missing or damaged packaging materials. These units are otherwise as new. The full manufacturer warranty applies. Click Here for more information.
Bag Capacity: 50 to 100 ci
Bag Type: Saddle
Worked well on a six-day bikepacking trip. The bag is lightweight and high quality, and it's nice that it's totally separate so you can pull it out for packing. The metal bracket and bag holster allow this to work with a dropper post. Note, however, that the instructions say not to use with a saddle that has carbon rails. Saddles with carbon rails often have a shallower angle on the back part of the rails also, which doesn't work well with this. The whole thing weighs quite a bit more than a simple bikepacking seat bag, but it's still relatively light. It was plenty stable and I found it fairly easy to set up.
The key feature for me was to have a seat pack that was easily removable. Most packs are designed to be attached to the bike so they must be loaded on the bike. I needed a pack that I could use everyday for commuting and was easy to take on-off the bike to carry in and out of the office. This has all the features of other packs but with the added convenience of being able to pack it off the bike. Other great features include the air valve to compress the bag when loading (absolutely required), and the ability to mount on a dropper post, if needed. Bag is high quality and waterproof. The mounting sling is very sturdy and easy to load/unload.
This pack has plenty of storage capacity and is very well built. It's allowed me to ditch my backpack for a more comfortable ride. I would recommend this product to anyone that is looking for great storage capabilities with an easy on, easy off attachment system. So I'll just say that it's not only highly functional but cosmetically appealing as well.