Well I was trying to get either the front or the back of the door card in first, with a view to subsequently easing the rest it in along the door afterwards. The rubber seal kept getting in the way with this approach tho.
What I ended up doing was lining the whole door card up against the lip in the door that's covered by the rubber seal. I then applied extra force along the top of the door card to compress the seal and allow the card to get past it, and once I'd done that compressing bit, I pushed the whole door card down in one go to seat it.
I've not explained it very well. But the key thing (for me) was to manhandle the door card back in all in one go, as trying to finesse either the front or the back end in first got me absolutely nowhere. Good luck! And make sure the door lock pin is lined up!