I suggest Golgotha, where it was already before - it's near worldmap center, empty for the most of time, visible for everyone (unlike SAD for example). Dunno much about technical issues, but it requires only to spawn shitload of stuff and to take care that no one will leave with any gear.I won't participate this, but I remember that many people liked it a lot.
2) Hold-up/hijack: that should be an easy one to make at least.. players get an alert, something like 'you have learned that a strongly guarded caravan transporting a large amount of cash is headed from NCR to San Francisco', then a GM leading an actual caravan with this brahmin carriage and some guards goes in the announced direction, stopping for a few minutes in every square. So there's the yellow circle on the map and any player can enter the location and try to rob the caravan.. The caravan starts with e.g. 10k caps and carries on whichever loot they get from unlucky attackers. So if the caravan is finally killed, the successful attacker gets the initial reward plus additional spoils.. and/or the keys from the brahmin carriage. If the caravan reaches its destination, well good luck next time:)