I said I'd post back in 6 months to say how things were going. Well, I suppose you could say I chickened out really. I removed the box about a month later. I just had images of me being stuck at the side of the road trying to get this box out before some BMW service guy came
I had one before in an Audi and it was a doddle to remove. Saying that, I still have it here in a box and I'm tempted to give it another go but the weather isn't permitting right now.