for pure afk i use full guthan with a guth booster > haunted mine/what lies below/vamp slay/tree gnome/lost city on normal rumble. The exp isnt great but its fully afk. Also you could use full dh with pray or absorbs and ovls using mtd booster on hard rumble. Edit: btw the dh method is semi-afk as you have to top up ur pray or watch for your absorb pts and top up on ovls. The prayer method i prefer as i get more pts out of it using an ancient mace spec which recharges your pray or an sgs if you can afford. With sgs and ancient mace there's a powerup called powersurge which gives infinate spec for a limited time so you can keep ur pray at max or if you prefer use a gmaul for instant spec