How did you handle making the moats?
I am working in Gimp as it follows.
1. Open new file size 1024x1024 pixels, in RGB Regime. This is Layer 1. Fill it with colour or water of your choice.
2. Open As Layer the file mount.tga, which is essentially the grass . This is Layer 2.
3. Open as layer the photo of the region, with moats, resize it properly, make it semi-transparent.
4. Make Layer 2(mount.tga) active, using Lasso or better, Path tool, select the moats. Change it to the Selection. Delete the Selection, and youi will see the moats water. Save these three layers as *.xcf file so that you may change the water colour, if needed.
5. Make only Layers 1 and 2 visible, join these layers and make them new file -e.g. BrestFort.tga.
6. In Unlocked FMB, use the file BrestFort.tga as a texture at proper place.
Btw, there is some trick in precisely placing the texture at the proper place, but it is common with the use of other textures.
The above procedure was used after the re-drawing of map_c did not give satisfactory results, because of moats being very narrow, the size of the whole island there is less than 800 meters.