And move the Map room to the base? Then why have towns?
you have a town for a place to have a battle at..
map room stays where it is.. keep town down % where it is.. rolling hordes would need to watch their newly captured bases until enough buildings popped, lest they be stolen right back.
It would take less people to take a base..
If people are as tired of hordes as they say they are, you make it easier to take bases, not harder. I guarantee the group sizes decrease, more bases change hands, more combat ensues, etc. etc.