Havening spent more then a few nights fighting like heck to take or keep a base that was being actively defended, i would say that it is already pretty hard. Sure you can sneak a base, or hoard a base and beat it down in minutes, i don't know that the placement of the map room really matters in either case.
If you sneak it all you have to do it take down ack and vh, then vulch, which isn't a whole lot harder then just downing the town.
If you hoard it the ack and vh are usually going to be primary targets anyway. If your goal is to make it harder, change the number of troops required to capture or shorten the time it takes for base/town objects to pop.