ah, got help to hold base down whilst I fitted the nut from underneath, otherwise it just popped out before I could get the nut on.
only had to pull top parts down/loosen a bit on b & c pillars.
I found hardest bit was releasing the old aerial FM connector, no room at all & you can't see how to release it, but desperation and brute force won that one.
then when punching C pillar black thin anchors back in, they would miss their mating holes
.........must be easier the 2nd time