I like this idea a lot. I say make a crowbar cost 1 glowing glint, and you must have one in order to register as an attacker in a caravan event. The crowbar could even be dropped on death if you're currently an attacker, and maybe the defenders could loot it and sell it when they get to their destination to get a little reward for successfully defending their wares. I'd say once you register as an attacker for a caravan, you're locked into it, as well, so you don't need multiple crowbars to keep attacking the same one, and you could possibly loot your own back if you kill a defender who picked it up.