For sale: an Exped Adventure Dry Sack mesh backpack, without the liner bag. This pack is 2500 cubic inches/25 liters and was designed to mate with a waterproof stuff sack. It has 3D mesh shoulder straps, multiple loops for a bungee cord array and d-rings to attach a waist belt. It is roughly 12" diameter and 14" tall and weighs 8.4oz and is in excellent condition. I have two at $25 each including US shipping and PayPal fees.

Here is the factory photo showing it mated with the dry sack liner. Note the integrating buckles at the top. You may find other dry sacks with mating buckles, they can be used as a compression and restraining strap across the top:Note the D-rings on either bottom corner where a waist belt could be attached, or they could be used to lash the pack in a boat.
To give an idea of volume, this is the pack with an uncompressed 20F synthetic sleeping bag stuffed into a trash compactor bag. I will include a new trash compactor bag if you like.
Using the top strap to restrain gear: