That makes things bunches easier.
Novus Mane is currently a vassal of Florum, generates income from fishing, and is located in Flanders. About 3 days travel from DePanne. Assuming its coastal this, irritatingly, puts it smack dab on top of Spider's Palace.
So, I say that it is actually located IN/Near DePanne, at the very northwestern edge of Flanders.
Note that this implies a close geographic connection to Florum.