This Brotherhood of Steel safehouse (SW of Camp Forlorn Hope) requires a key to open (access through drainage). Anybody know where I can find the key? I really want the Repair skill book that's in there.

The guide doesn't address the key at all

It was unlocked when I went there.
According to the wiki it only unlocks when you join the BOS, it has no key.

Dam it.

Alrighty then, thanks!

It never unlocks. It was locked in the latest patch for some reason. As of right now there is no way to get in there.

Joining the BOS gets you the key to the other safehouse, not the one south of Forlorn Hope. There is NO KEY to this anywhere in the game (you can check in the GECK) so we can only assume that it is locked for a reason (eg the entrance to a future DLC or somesuch)

Then surely somebody on Pc could unlock it?

Yep. Simply go there, hit the console button, left click on the hatch and type unlock. There only note worthy loot in there is a skill book for repair. The hatch was open until the latest patch which locked it for some reason.

weird. I was wondering how to get in there as well. I did all the BoS quests and it was still locked... which led me to believe there were more BoS quests... obviously not, lol

Is this the shack where Father Elijah likes to leave his secret messages for Veronica?

No.