B7 Cabriolet Roof Storage Box Removal

I’ve managed to source a replacement roof storage box for my Audi as my current one has been repaired in the past but has broken again. It’s the box that sits in the boot and safely reduces the loading area to allow the roof to stow. On attempting to remove the existing one there’s one nut that I can’t access. It’s on the passenger side and is the lower of the four on that side. Has anyone got any experience of this or knows the procedure? I’ve gone as far as removing the panels that hide the mechanism and taking off the shelf from its runners on that side but I still can’t see the nut to undo it.
I’ve googled my issue but to no avail. I partially stripped back the replacement part in an effort to see if I could figure it out but am wary of going further and damaging it in the process. Any advice or guidance is greatly received. Thank you

Sveneng

I must admit that’s what I’m leaning towards and then leave it off when refitting the replacement.

Just to update this for anyone else who’s removing the roof storage box. I believe the Audi tech method is to raise the rear deck which gains you access to the top of the box. There are two star screws to take off on either side and then two people can lift everything other than the supporting side plates out of the boot. This should expose the final nut that I couldn’t get to.
However when I tried this on my replacement part I still couldn’t get it to separate. In fairness I didn’t force it for fear of damaging it.
So I did as LaurenceH did and after measuring the exact location from the replacement part drilled a 15mm hole through the left hand plastic side plate to gain access to the last bolt. After that it all came out with no issues. I’ve fitted the replacement box and left that nut off.
When I get some time I’m going to strip the old part down fully to see if I can refurbish it and also to confirm how to remove it properly.