Using PlayerPrefs to save a C# Generic List

I have a list of Times taken for you to complete each level.

 [SerializeField] public List<float> BestTimes = new List<float>();

But i can't figure out how to save and reload all its floats. I'm currently using PlayerPrefsX(ArrayPrefs2) by doing this.

to save: PlayerPrefsX.SetFloatArray("BestTimes", levelselect.BestTimes.ToArray());

to load: BestTimes.AddRange(PlayerPrefsX.GetFloatArray("BestTimes"));

But the list just returns as all zero when i try and load them? Any help? :D