Door Card fixing bolts/screws

[Rossi17]

Hi,
Would anyone know what screws/bolts to use to fix a couple of brackets to the inside of the tailgate?
I want a quite strong fitting and I assume it’s only a door card what’s on the inside of the tailgate
Thanks for any idea’s.

 

[Deaky]

Take the hardboard off and you'll see a few places you could fix to. Rivnut and bolt would be my preferred choice

 

[Rossi17]

Rivnut was the answer, thanks Deaky