For those who are challenged by the Gmax/FSDS Instant Object Studio runs as a Flight Simulator module and lets you design new scenery objects directly in the Flight Simulator 3D view. You can create several predefined types of 3D shapes and then edit and arrange them to make a scenery object. You can move, rotate and stretch individual parts of your model, bend them, apply different textures, create holes and indentations and apply other transformations to make even the most complex objects.
http://www.flight1.com/products.asp?product=insobjstu
http://www.flight1.com/products.asp?product=insobjstu