You'd need a high level cap for the caravan guards (15+)
What do you mean by this?
Lv21 characters can't join?
Like an amusement park with rides that say "You must be this tall to ride this ride?"
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Also- Radio Beacons!
It would make sense for caravan traitors to radio to their accomplices to attack; even better: a member of Raider Faction could radio for Raider NPCs!
(Would have to assimilate into regular population first by waiting for reputation from joining Raiders to "heal" plus do good deeds/etc. to build rep.)
There could be "Anti-Caravans" that Raider characters can join at the Raider bases. Hopefully these will have a chance of intersecting with Player Character escorted caravans.
Perhaps Raider Mercs could also be hired at the Raider Bases.
If caravan people with radios can be killed fast enough, perhaps no rep loss- it will just be a mystery!
"Swallowed up by the Wasteland".
If it happens too often on a route, more patrols will be seen, guards improved, and "frequent survivors" will be blocked from joining future caravans.
(Have a caravan cooldown timer that resets after a successful escort mission, plus maybe other things.)
I am very definitely in favor of caravans/etc.
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Also there should be Train Station Quests which will allow characters to enable telegraph bank transfers for themselves.
Not sure about raids on trains- there is supposed to only be 1 train, but maybe that can be changed through questing for parts/etc. Also, there should be a laser turret on the train. Just in case.