How to share a terrain in a group

Hey, Me and some friends are working on a game, where we spilt out the work. I have done the terrain og some other have done some programing, now weneed to share the terrain between us. I have tried to use this http://wiki.unity3d.com/index.php?title=TerrainObjExporter#Usage but it didn't work. the error we get if we just copy the we gets a lot of null on splat alpha errors some that I even have in my project.

so what Can I do?