Just thought of this to add. You can select your object in your scene then go to top view, select altitude render (make sure you zoom in on your object so it'll take up most of the frame). Once it finishes rendering then export picture to what format you want (.bmp or .tiff is probably best) then edit in your image editor and import into terrain editor. This is how I did the wheelhouse on my boat, as well as the yard arm (which is 2 cones rendered in altitude then skewed in photopaint and imparted back into terrain editor).