Can you be more specific on what these sheds are for.......and what bait you were using,
I would be more inclined to proof them then go and bait where you are thinking they are coming from, I would also be sweeping up any feaces and looking to see if you start to get fresh faeces around, 4kg is a lot of bait.......you may of dealt with the main problem and just have a few stragglers left behind.....stick some traps down