I need to do some experimenting first though, is there a non-permanent or event semi-permanent way of doing this ? I think I can make the shape of a Kamm from what I have (but I will need to read up on dimensions) and then do some tests.
My first Metro (from Grandma TBH
) had this kind of spoiler on the back
Which is what I was planning originally but I'm not sure it would make a serious difference.