I had success without rooting N7 and using OTG cable to connect my Canon S100 camera directly. (N7 is rooted now with OTG Helper installed)
One device I found locally was a portable Cloud Wifi, able to perform as a router, access point repeater and battery charger. With this device I was able to create my own private network (without external 3G or Wifi) just the Cloud Wifi and N7.
All I need to do is connect portable storage to Cloud Wifi device, since it has it own internal battery it is able to power the USB HD storage. From N7 select the Cloud Wifi SSID and I am connected. Now I am able to transfer photo using OTG cable to my camera and wireless transfer file to portable HD storage.
One of the best setup with Cloud Wifi, my partner or others can connect Wifi to the portable USB storage and view media files from it.
If you like to know more this is my BLOG POST link (just started this blog for personal reference)