|iKube porta cabins|
I found them on a spanish wargaming terrain site called Toposolitario which also has an English translation. There is a video showing how to put them together in under three minutes. This is a simple paperfold exercise. I prefer to put a foamcore chasis inside to make them a bit more durable and survive transport in one of the terrain boxes. It takes about ten minutes to put them together with a frame inside.
I will be putting them on a card and sculpted base when I have finished doing the other four I have to do.