I think as a technician/engineer I should know how to make a round hose oval ;-)
But round would fit better (same scope)
Second problem is the position of the outlet. In the vectra box it´s a better position to mount like you did.
Maybe I´ll just order and have a try. If it doesn´t fit I still can buy another box. I already found all parts in Ebay 🙂
By the way: Whats a jubilee clip? Don´t know this word. Could you explain for Germans?