I don't have NL2 open right now but I will try to recall from memory
Make your object and save it into your park folder,
open up ''new NL2SCO'' in the scenery tab,
click on ''New'' and name it whatever you want and save it to your park folder.
Click on ''3ds model'' (or something like that) and select the 3ds file,
If you made it in sketchup, go to the advanced tab (in the NL2SCO) and check ''fix ambient materials'' which will ensure that shadows work properly
From there you can either add it into the editor as you would any other object, or continue playing about in the NL2SCO editor
Hope that helped and I didn't interpret your question horrifically
I'll provide screenshots if needed