Hi All.
I have to replace the winder box for my roller shutters. The old box was larger at approx. 14.5cm high, by 9cm wide. The new box is 11cm high x 7.5cm wide. Photos of the box in the space, and empty space below:



There is only a stud to attach to the left and below. Nothing above or to the right. The previous one was only attach on the left and bottom, so that seems fine. But what I'm not sure how to do is patch the hole to the right and above. One idea I've had is to attach a piece of pine to the wood below and attach the box so that pine. A 19mm piece of pine just fits below. But it won't fit to the left of the box so I can't do the same there.
What I was thinking instead, is to attach the box directly to the stud on the left and then attach this to the right of the box to fill the space so that's it's easier to plaster over https://www.bunnings.com.au/macsim-72-x-100-x-10mm-black-packing-shim_p1044804. Can I drill through these and secure them? Can these take some load if I attached it to the wood on the left, and then attached the box to it?
Does anyone have any smarter ideas?
On another note, once I opened up that space, I found a ton of long grass and one or two pieces of paper packed into there. There were no animal droppings though. What could that be? Rats nest?
Thanks
Regards
Itai