I just completed this on Saturday. I used a void shotgun and a void rocket launcher. Basically you have to play passively paying very close attention to your radar. Run away from any fights that are not within your shotgun/melee range or switch to your primary for those kills. To get the void kills I basically watched the mini map until someone was in range, always start with melee to take down shields than one blast from your shotgun will finish them off. Took me about 3 to 3 1/2 hours but it was well worth it. Thorn is absolutely amazing in pvp, I have the last word and I will take thorns DOT over last words rate of fire any day.