But the Wesker and Shaggy ideas combined could work: to siege a pob, need a specific weapon, NEMP-like, that to be get need make an admin request (same needed to build such base) and similar level of RP and workload. And make amount needed equivalent to base core level.
Maybe instead, make a Titan feature? Just those can siege pobs, and can only be get trough event, like: i want siege x pob, make an event, supply it, grab ur Titan, kill pob, Titan poofs. Want siege another? Work again. That even would help activity.
That way, isnt anymore pob owner working a year to make a core 3, involving a faction to it, spending billions, countless hours of trading/rp, to be destroied in 2hs, if the "cool" attack fail during day, at 3am when no one around.