1) Enable the mission editor (Start Blockland with -mod editor)
2) Move your DTS to: Blockland/base/data/shapes
3) Start a game
4) Press F11
5) Press F4 (Enable the World Editor or something)
6) Click on the little (+) sign
7) Browse to Static Shapes > base > data > shapes > yourmodel.dts
8) Double click and it gets spawned at you crosshair.
9) F11 Again to disable mission editor