The possible 4th Hidden vendor location being discussed
So I started delving into this mystery as it was addressed earlier (and removed once it got RickRoll'd) and I have come up with a possible answer.
Apparently there was a 4th hidden vendor at Heaven's Gate. At heaven's gate, there is a boat to the left, a dock straight ahead, and a cabin to the left. You were suppose to clear all three areas, then at the intersection of them, a vendor truck appeared and was under attack. Kill those raiders, and now you can use the truck.
However, I just spent 30 minutes there trying to get it to spawn and it would not. Here are probable reasons as to why:
1) It was originally a vendor truck. All hidden vendors became NPCs in a patch.
2) It could possibly count as one of the vendor emergencies, as we know some emergencies actually are triggered by doing other emergencies. There are/were (as I haven't done any since the plague) some in San Fran near the Overpass like this that gave faction.
3) The dock enemies (not the cabin or the boat) were changed during the Pied Piper missions to Rogue E-Rep soldiers. Upon reaching Heaven's Gate, there were still E-Rep enemies and an electric hellbug on the dock and raiders at the cabin and boat. Maybe by not having the raiders on the dock, you cannot access the vendor.
4) Ever since the plague hit, I have not seen ANY of the normal travelling vendors from the defend the vendor emergencies. Maybe they (and Heaven's Gate) have been taken out of the game during the plague.
One thing that did catch my eye: Behind the shack on some crates was an odd device with a glowing red light. I took a picture but I freaking HATE Windows 8 as it won't even give me an option to add it to the post.