Hi – one thing to keep in mind is that these areas are invisible on the inflated packraft, so don’t be reluctant to spread the Seam Grip or Aquaseal onto the tube fabric there, as any discoloration will not be noticeable. A thin layer spread wide should do the trick, especially if you have a zipper in your boat and are able to apply it to the inside. If there are folds or gaps in the seams, apply a thicker coating or multiple coats there to ensure you fill the voids.
When constructing a packraft I coat the inside of all those tube/tube/floor/reinforcing strip areas with Seam Grip spread out about 5 cm or 2″ from the seam on all directions (as well as coating the entire length of the inside of the seam strip), and since I started doing that I haven’t had any leaks.
As Kjetil mentioned, you can use an accelerator to speed up the curing time of the McNett/Gear Aid polyurethane products (Aquaseal, Seam Grip, Aquasure). Here, the accelerator is called Cotol-240.
I hope that helps!