Started something similar last summer for watering my garden but not wanting to use anything (except wifi) connected to the house.
Suggest looking at Raspberry pie projects. You probably know what the Raspberry Pi is, but if not, it's a pretty cool and inexpensive CPU board that you can use for amazing things.
But, I'm not recommending the Pi to you for your project, what I am recommending is to look at some of the Pi projects. There are people who have embedded Pis in external boxes, in hot/cold/wet environments, with solar and battery powered solutions. In some cases, they are amazingly ingenious and use things that are not expensive, or tell exactly what to order online, or what part numbers and products they use.
And finally, even if you get this setup working, how are you going to see the camera if you have no wifi? I am interested because I have a security cam system in my house. I use the Linux Zoneminder app, with some dlink-920 cams, and another with PTZ functions (Zonnix I think). The PTZ camera can use a Micro SD card, so perhaps that kind of option will work for you as well.
Have also seen posts in other forums where an external cam can be setup using a Deer camera. Haven't seen one myself, but there are apparently low cost systems intended to be left in the woods with decent battery life and some onboard storage and motion sensors to be able to take pics of anything that walks by.
Anyways, will monitor your post - sounds like a cool project.