hmm ill look in to giving you a solution for this. personally i feel like drawing a trace line every 3 second is very uneffective. but constantly drawing it can lower your fps(probably.). i would most probably go with the collision box idea but i guess ill try and give you a bp for this when i get the time for it.
you can also have a look at this and see if you can understand it yourself: WTF Is? Line Trace For Objects in Unreal Engine 4 ( UE4 - YouTube