GTA V Guide : Bugstars Equipment : Get the Van without Triggering the Alarm XBOX 360 PS3 PC
To get the van without being noticed drive around the dock to the back of the warehouse. Leave your car well away from the warehouse and sneak into the warehouse:
Take out the guy standing at the back of the van. Get into the van and carefully reverse as it is easy to drive into the ocean. Then you can drive away.