"Gripfill" is a filler/adhesive in a tube like a mastic sort of thing, it sets into a plastic. It was the nearest thing to hand.
I decided to glue the tubes as extra insurance as I'm unlikely to need that trim off again and I figured the more secure it is the better. If I do need it off I can easy cut the tubes away with a sharp knife .
The tube I used was much like you see for vacuum pipes in the engine bay, it has quite a thick wall and narrow inside so it goes on nice and tight.