Yay i finnally came up with something worth persueing, i did come up with it right? Even if someone else did i have some ideas about that

You could have a quatermaster ancillary, and alsorts of other ancillaries that could be derived from the howlong have you been in enemy territory trait, like if you took a new town or something like that after spending along time outside a city you get a "quatermaster" or something similar.

Also you could give him a trait based on what buildings were in the last town he stayed in cant you, you could say that a granary or armoury in that town dictates how good his logistics are, which could have an effect on the money he costs extra.