I shot a number of fishing shows in Northern MN and Canada. One of the things we did was use a large marine battery to power the camera for hours. That was an older tape-based camera. On today's cameras, a large battery like that could last all day easy. You will need to be very careful doing this. Consult an engineer or even the rental house if renting. You'll need to recharge everything- solar panels? Offload footage and backup? Any stays at camping areas in between? AC recharge.
My two cents.