GWX being a major mod which focuses on historical accuracy and realism more than many other things - removes the umark for a couple of reasons i can think of off hand...
1... it doesnt / didnt exist in reality
2... it makes for better screenshots if it isnt in the image.
I hate that your having problems... sometimes the only thing harder than installing a mod correctly is creating the mod to begin with
follow the advice of those experienced folks here and you will be sailing smoothly soon
good luck