I bought it. It is almost satisfactory, as the photos show.
The package - picture 1 - comes with 3 pieces of seal (2 push-fit sides with corner pieces attached and a self-adhesive bottom) and a tube of superglue to attach the little corner pieces to the tub, I didn't bother because it doesn't seal around that area perfectly anyway.
The left and right side are a push-fit over the lip, just watch out for any excess body filler - you have to cut it away. I was fairly lucky there, my Wednesday-build paid off again.
Closing the tailgate with just these on showed me there'd be a gap - not bad, but it's still a gap. I might try adding rubber later. You need to cut the bottom seal to length after fitting the little lugs from the corner pieces inside and then remove the backing and stick it to the lip. Luckily there's an angled section that the seal sits on and makes a good fit, but please sit yours in first and check the height. I stuck mine in with the smooth curve up towards the front.
Would I buy it again, knowing what I know? Yep. I am going to add some rubber to the tailgate itself and finish sealing it off.