Lmelamed - did you ever find a viable solution? I am wanting to do the same also.
Yes. I used the 2 following items.
Voltaic Systems V75 Always On External Battery Pack with Dual USB Ports - 19,200mAh
WISSBLUE Solar Panel Charger 22W 60W, Dual USB 2.4A 4.2A Fast Solar Charger
Has anyone said something about using 2 power banks instead of one? If not maybe that would work. Solar panel charges 1st battery bank then the 1st battery bank charges the 2nd one which is powering the camera. Have you tried this at all? Also did you say that for sure the battery bank will keep the camera powered for longer then the 1 day?
Better off to just use a larger battery bank. There is at least some energy lost in every conversion, so daisy chaining battery banks would waste a bit more power.