Finger & Toe expands their 15mm Garrison line with their Outer Works pdf.
From the website:
Outer Works is a 15mm modular set for building the smaller sci-fi fortifications found defending outposts, new colonies, or pump jacks beyond the pale of civilization. The set includes 1, 2, 3, and four inch walls, inside and outside corners for designing customized set-ups. There are also firing steps for each wall type and a gun emplacement for heavy weapons. Accessories include a multi-use accessory base that can double as a remote sensing station, a turret for heavier weapons for aerospace defense or fire support, auto-sentry guns, and a sensor pod on a tall mast.