Nice work Rene. Remember this area decays by dust dropping in to the lower cavity from the upper structure openings/holes. Moisture gets into the dust, sits there and rots the wheel well bottom. I open them up probably more that is needed for a restored car that will no longer be in the elements but I have never had an issue with strength or future corrosion. Here is a shot of large drain holes on a repair very similar to yours.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.