I feel like I created a Supply Depot earlier in the game with a flatboat with 4 elements. I am now in June of 1862 and am trying to use flatboats to make some depots down the Mississippi but it seems no matter what I do the icon for creating flatboats is greyed out. I tried some areas where I had military control on both sides of the river to no avail.
I think you can create supply depots with flatboats but there is obviously something I am missing something.
Thanks for any help.
Jack