Wish you well with the drilling.
I would advise that Strada tailgates are well known for corrosion. All starts at the window rubber lower corners. The mid sections (spoiler area) have been either fine or rot sections. The lower tailgate vertical flange is also a rust trap/issue but this is generally dictated by the window and spoiler water ingress/access points.
When you have drilled the holes do:
o clean and rust primer treat the holes
o top coat the holes
o waxoil / similar treat the holes before fitting the spoiler
o fit spoiler
o waxoil / similar treat all areas after fitting the spoiler