Complicating factors are, that mesh objects can only be 64x64x64m in size and that they take a lot of prims. In order to cover a complete region with one environment, I had to use 25 meshes that take about 900 prims. Optimization of the meshes could reduce the prim count, but I hardly think decreasing it to less than 450 is possible.
You're invited to take a look. Please beware: you need a mesh viewer to be able to see the environment in it's full glory. You can use Linden Lab's Viewer 3, or the latest Firestorm viewer. Don't hesitate to comment on my work on this blog or on my profile wall!
Follow this link to visit the mesh environment..