Over at the OpenRelief project we have been considering the issue of powerplant as well, and have come to the conclusion that gas engines probably work best for all-weather endurance. Our current airframe (http://openrelief.org/pipermail/developer_openrelief.org/2012-July/...) is being tested on electric, but we will be moving to a 50cc engine as a build option shortly.
Over at the OpenRelief project we have been considering this, and gas engines probably will work best in wet weather. Regarding the airframe, material like foam and balsa might have some problems in wetness and wind, so we are currently prototyping using plastic, aluminium and a small amount of wood.
Bear in mind that the GNU GPL was written for software. It is probably best to use a license designed for the specific purpose in mind. If you want to license documentation, then things like CC-By-Sa make sense, though when it comes to Open Hardware as a field we do have options like TAPR or the SolderPad license.
Well I wish you all the best with that project but that list of figures looks a tad optimistic.