Ya you need a crew. It is possible though to do it by yourself. I did it three times by myself. If soldiers attune to you just run, they will disengage pretty fast. Kill the soldiers you saw attune to you one at a time, then quickly search the barrel. Then you will know not to search that barrel. NEVER EVER search the barrel by the building in the middle of the Kingshead town. If you do, almost every soldier in the field will attune to you. If you can't do it alone then just do what Kirandwilfort said-find a crew.
