Google Sketchup requires either Blender, or Milkshape, you're boned either way.
Blender is quite easy to model with, but not so easy to export into Torque Shapes (DTS).
Milkshape is VERY easy to model with, add armatures (mountPoints, MuzzlePoints, etc.) and export with.
I'd recommend Blender if you're more advanced with that kind of thing.
Milkshape if you're new to computer modeling.