You only need 5, here's the locations of 12 with a lvl 2 Garrison (ALLIANCE)
1 Under the shelter to the right of your town hall (near your supply pile)
2 First crate to your right as you follow the path into your Menagerie
3 In the shelter of your pet menagerie to your left
4 Stand in the battle ring of the Menagerie and look south. See the tree in front of you? The crate is against the wall to the right of the tree
5 From the previous crate, follow the wall to your right, pass the dirt pile, continue following the wall to your right. You'll drop down the slope, the crate will be in front of you.
6 Keep going straight, crate next to outhouse
7. Walking into your garrison, look to your left, crate behind the guard house
8 Walking into your garrison, in front of the small plot to your right
9 continue walking into your garrison, just to your left as you enter town square (next to Eileese Shadowsong)
10 right side of the base of the steps leading to town hall
11 Medium plot to your left as you look at town hall, to the right of the steps leading up to that plot
12 When you're at the base of your town hall steps, pan the camera to the right and you'll see a crate in the field