The bottom fuselage skin must be reinforced for the transponder antenna, time to design and make another bracket.
A nice article to read about antenna installation is this article.
The design was done in Oneshape:
Oneshape has a handy feature to create a drawing from the designed part:
CNC fabrication done:
After bending and deburring:
Perfect fit from below, the flanges make sure the forces are distributed to the stringers as well and not only to the bottom skin:
Inside view:
