It's probably too late for Bannerlord to mess with the mechanics of these groups...
But i think there are interesting ways of improving them. They seem like nomadic clans of brigands or tribes from the wastes. But because they have no economic basis, I can't think of them as nomadic. Rather, I tend to think of them the way I think of
free companies - or
military orders - Professional incorporated firms or organisations who sell or lend their arms rather than physical products.
As such rather than a base or encampment, maybe an office or offices in either their region of origin or region of employment would be more appropriate. Where their accountants and book keepers would theoretically be located (and might sit in the city view next to merchants and gangs). Their office would obviously need to pay rent or a fee to it's city owner to stay incorporated there - making them attractive to host.