In 2014, for Xenophobia, I made such a base. Neither the floor nor the walls can be seen until the shooting begins. It was very difficult, but very interesting.
But Predators are watching my soldiers ... This is certainly a joke
Sorry for my English.
I found the solution.
It was necessary to copy fresh version of ModManager from assets/mods/xce folder to root Xenonauts folder and run it from there.
Maybe it will usefull for anybody.