Attacking a fortified position is easy, you need to remember two basic ideas.
1: Impregnability works both ways. If it's hard to get in to, it's nearly impossible to get out of.
2: bunkers don't move. If they do, they're called tanks.
If you can avoid the position, you should. If it's unavoidable for some reason, you can control the players inside of it by denying them access to windows, doorways, or shooting lanes with your paint.
There's a basic primer there. Go get 'em.
-Tyger