I'm attempting to create a depot in Morhange. The rulebook tells me that I can do this by converting Supply Wagons but the tooltip I get when trying to do so tells me that I can't due to either some structure in the region, insufficient control, or insufficient units of the right type. The only structures present are a Level 1 Town and a railroad; I have 100% control; and I have three wagons when the book tells me I need only two.
Enlightenment please.