The Bulldogs are sheltering in some 3d printed terrain from the company Endertoys Terrain.  They are US based but sell some items via Amazon.  Their main website is:

https://www.endertoysterrain.com/


This one is from their Siege The Shore set which also comes with some sandbags, tank traps and ammo crates.


It does appear unfinished but some foam board could be used to construct a roof I suppose.


 The range includes contemporary, sci fi, fantasy and a range of dungeon terrain.