They're all garrisonable, I use them a lot, actually.
Try to use the impass overlay.
Go to Overlay (fifth bar on the top of the screen),
Draw Overlay Map (somewhere in the middle),
Draw Impass Map
Now you will red and white/invisible blocks. The red blocks mean non-walkable and non-drivable spots (blocked), so no units can use these places. The white/invisible blocks mean that the units can use these spots, but keep in mind that your units won't be able to come to such spots when there are red blocks surrounding it.
When you see only white/invisible blocks when you clicked the Impass Map, you can reload it using SHIFT+F5. (CTRL+F5 is the shortcut for Overlay.)
I hope that my comment helped you a bit. Try to keep the entrances of the buildings white-invisible.