Such patience! :)
Right, by my reckoning, there are more people wanting a closed FB page than those that want WhatsApp.
In all honesty, it will take you seconds to create a FB account. You can use it for the purposes of this trip and then dump it.
I'm by no means a Facebook expert, but I've now PM'd all interested parties with the closed FB group details.
If there are any late comers, please do shout :)