Awesome! I had been working on a similar project couldn't figure out the snow on the trees for the life of me! It's great to see how you approached it. The work look great! Thanks for sharing your process.
I believe author would be surprised that it's not american, but soviet bunker :)
3D artist Bryce Szandro released his hard surface kitbash set featuring 20 pieces that can be reused in many ways. The pack includes original Max and Zbrush files for you to edit the models.
You are free to use this kitbash set and modify it how you wish for personal and professional use.
You can also email the author if you have any questions or suggestions.