Sorry, been busy moving and junk. Hope this isn't too late. If you already have the Nav II, here's the trick. The seams on the side bladders must be positioned straight up and straight down. If you don't the tube will roll inward towards your legs. Won't effect safety or anything, it's just really annoying. Getting the seams right is a big giant pain. It might take hours to get them perfect. Also, be very careful not to open the valves too far. When is too far you ask? When the tube starts leaking after you close them. Or maybe they just leak period, I don't know. I finally got sick of leaking valves and bought a different tube.

If you don't have one yet, get a Kennebec by Trout Unlimited. They are cheaper, easier to setup, easier to transport, and have twice the storage. I think Sporstmart even carries them now. I have the Gallatin, by the same company. I'm going to get the Kennebec soon though. It is smaller profiled and has a stadium seat, which will support my back better, and the back bladder is small, so it'll fit in my car better. Both are great tubes though.

Good luck,
Amish Ed