When I had to export a .mdl file I used the 3ds format, I think. However, I'm not sure if UVs stay intact when doing this.

By now I always use blender to create and edit models. When I'm done I export it to fbx and import it in MED.
I think it's a good habit to do it that way, since you don't have to convert models from MED to another filetype (which is always really annoying).