Hi Perrin,
Don’t worry – the zippers are very tight to begin with, but will loosen up over time. They’re especially difficult to open before they are mounted, because you have very little to grab on to. If you want to try them out before they are installed in the packraft, you can clamp one end of the mounting fabric in a padded vice or vice grips and pull on the T-zipper handle. Thread a dowel or something through the webbing loop to make a larger handle, if necessary.
That first opening will require a lot of force, but the zippers are very strong, so you shouldn’t be able to break them if you pull steadily (don’t try to jerk them open though).
After it’s open, adding the silicone lubrication to the zipper will help, and after it’s been opened and closed several times it will start to loosen up. It will always remain fairly tight though, compared to a normal zipper.
My recommendation is to open and close the zipper a few times before installing it, but to wait and lubricate it after it’s installed so you don’t risk getting silicone on the fabric, which could interfere with the heat sealing.
Cheers!