Hello,
So first of all, you can certainly drill holes in your trailer to screw something, as long as the safety and stability of the trailer are not affected, no problem.
I'm assuming that the "wooden wings" are only there to support the TH. Then they belong to the cargo as part of the load securing, so the TÜV should agree if it increases the cargo security.
The only thing they could complain about is the material, from the feeling I would say that the TÜV would prefer to see something of metal. Ask best your TÜV Examiner.