Rerod, you can do an energy audit finding out how much everything in your rig draws for power. Get a DC clamp on amp meter, remove fuses and turn off breakers (A Trimetric, Victron or other permanently installed battery meter works also). I then add each fuse back and take an amp reading from the positive battery wire with the clamp on. Once I'm done, I figure out how long I'll run each device per day of camping and that gets me my total amp hours. It takes a little while to accomplish this task but gives me an excuse to be out in the rig. :)
