Revelate Designs LLC Viscacha Larger one of the 2 that he offers.

Don't be fooled by the color of the bag. It is in great shape. It has been sprayed with a water proof material in order to keep things dry inside.
Please see the inside of that bag and you will see its in great shape.
It retails for $130.00 get it today for $81.00 + $5.95 Priority Mail™ Small Flat Rate Box
Note
It does have a small spot where my tire rubbed the bottom. I covered it with stronger then Iron Man tent tape. That was 3 years ago and again looking inside it does not have any issues.

Here is the website info./

he big bag for big trips, the Viscacha™ (vis-KA-cha) does it all. Take it on the Great Divide Route, the Iditarod trail, or long day trips. This is *the* go-to seat bag for big adventures! Proven time after time in the longest and hardest endurance events on the planet, be it dirt, snow or pavement.

The roll down opening allows the bag to easily expand or compress in volume. A removable internal compression strap aids in packing and closure, seat post gripper wrap attachments. High density foam stiffens up the front and a flexable plastic bottom sheet gives support along the bags length.

Dual position saddle strap allows for proper fore-aft positioning depending on where your saddle rails are clamped to post.