I don’t have a part number for the neoprene weatherstrip, but it needs to stick out 3/8”-1/2” from the adhesive. You can find it in rolls at big box and a quick search at retailers.
Quick tip on the strut/rods and brackets that hold up the top. They love to vibrate loose. Tighten the knobs as...
Had exactly the same problem with the dealer-installed Ford Bakflip on my new 26 last month. Check adjustment as ZABSMAV says. Mine was installed too far forward…move it back as far as possible without the frame interfering with the tailgate…that gets the back weatherstrip engaged a little...