Locking a metal gate with a deadbolt
A deadbolt doesn't need a strike plate, because the gate is swung with the bolt retracted, and then using the key the bolt is advanced into the hole.
You can use the strike plate if you want and screw or weld it in position over the hole.
For the double gate consider organising the ground pin so that it interferes with the deadlock pin or the other leaf of the gate so that it can't be withdrawn until the gate is unlocked