I usually just take a bow with as many arrows as possible when I am attacking or defending in a siege as I find this to be the most effective method for getting a lot of kills and it's great for leveling Athletics as well. I can't help but notice that when you are a defender you have access to arrow barrels making it significantly more effective in a siege than when you are defending as you inevitably run out of arrows. I think both sides should have access to arrow barrels, and I feel that ultimately it makes logical sense that in a real historical siege both sides would be well supplied with arrows. I am hoping this can be added in a future patch. Cheers and thanks for all that you guys do!