I got a new front fibreglass XR extension from Canberra Body Styling but it's all hollow with no internal mounts.......Do i use a s**t of SikaFlex Or screw it in the bottom and SikaFlex the ends or What???

Two screws around each return on the wheel arch and the remainder on the underside.
You'll see imprints in the glass where Ford used to mount them.
No Sikaflex needed.
Cheers, Bob

Okies Bob! It seems to fit very well too .....thanks to you.....cheers!