It's locked up, so it seems they don't want to face you. There are two ways inside: via boat and by driving a car over the wall by the side. The latter is the preferred method. Call a well armoured car like the Stampede and drive into the centre of the compound.
Drive into the compound and take out the few guards, then get out of the car and enter the building. Now would be a good time to use blind rage, as there will be gunmen on top of the shelves. Kill the manager who should be in the top office or along the top there somewhere. Now shoot the guys coming through the doorway – there will be a lot of them.
Once out take cover and take out the guys on the ground, be aware of the snipers on the roof tops. Now that they're out of the way, there will be more attackers arriving via boat. Get in your car (or one of the left over cars) and head down to the dock. You should make short work of the boats, and this is another good place to use blind rage.