Setting Initial Size of ToolWindow

I've got a ToolWindow that is (ultimately) inside of an AutoHideLeftContainer. I want to set the initial width of that ToolWindow. The only thing I've been able to find that appears to work is to set this property on the ToolWindowContainer:

DockSite.ControlSize="500,500"

Is this the preferred way to accomplish this? Is there an easier/better way?

David Mullin