Cut out rot at bottom and made a couple of repair pieces to fit in.

Will repair in two parts. Restore inner flange with small triangular piece and then weld in repair piece you can see in photo. The holes to the left will just be filled with weld and ground back.

This side will also be repaired with two pieces. One to restore inner flange and then angled piece to fill hole. The repair pieces I fit to inner flange will be bigger to start with for cutting down after grinding welds flush.
The repairs to the top should be easy as it has not rotted out to the curved section of frame. Both repair plates will be about 15mm x 40mm.