In FT3, use File>>Save As with type Special MDR. This type of file saves the whole world in the Equirectangular projection without any sort of collar. Saving a regular MDR file will get exactly what you see onscreen, including any extra parts that are not on the world's surface.

There is a relative bug between the two programs that requires you to flip the world vertically in Wilbur, do your processing, and then flip it vertically again before importing it back into FT3. It's a long story about a GDI->OpenGL conversion and doing one-too-many cleanups, but we're stuck with it now. BTW, the Incise Flow code is the same between Wilbur and FT3, but I never got around to porting the precipiton erosion to FT3. Maybe FT4? Who knows...