How to make rear storage box for a BMC?

I stumbled across this picture of some BMC TM01s with custom rear storage boxes on the frame. Anybody know how this was done?

https://scontent.cdninstagram.com/hphotos-xft1/t51.2885-15/s640x640/sh0.08/e35/12362493_816280741832739_642883255_n.jpg

OMG their bikes are so kawaii desu !!!

I am more curious about the sex sign behind the top bike.

Ha! Yeah, there’s definitely a LOT more going on in this photo than expected.

Yes, I think I’ll draft along with this thread, could get interesting !!!

Through some reverse Google-Fu, I found the owner. Kai Hashimoto. Page is here.
http://pictigar.com/media/1142657957307784043_2283036701

Looks like the bontrager draftbox II… There was a thread a while ago on a sweet shiv that had something like this retrofitted onto the rear. I suppose you could install threaded bosses or, if I recall correctly, doublestick tape along the seat tube and some kind of crazy thread held to the seat clamp.
Don’t know if this helps at all! Good luck!
https://shop.sunrisecyclery.com/item-picture/432066/picture