Need advice on additional tailgate lock for '01 SC.
Is factory lock good enough to prevent
theft or should an additional lock be used?
McGard maybe?

 

IMO I believe it to be good enough to prevent [tailgate] theft. Sure, there is always someone who can 'get past it', but that same person can get past your door locks and raid your interior.

But, what happens when you forget to lock the gate? Thats when the McGuard lock comes into play.

While your at it, go ahead and get the locking gas cap.

 

I wouldn't know how good the lock is. My keys don't work on the tailgate.