Something like this?
http://www.radioparts.com.au/product/03296520/c12-40dg-12v-40amp-deep-cycle-gel-battery-century#.WroBB4huaUk
deep cycle doesn't help with only 8watt/hour power drain, any cheap car batterie will do
I was actually thinking of something from a truck or a golden holden 3.3 or a series of ups batteries, not a batterie the size for a toyota yaris..but I'm sweet with this, are you?
this would give you a 1 day buffer safely and 2 days until the batterie is dead with no charging.
Don't mean to boast but sunshine is good here, in Byron Bay, the most easterly point of Australia. Average temp is 75F and we get a mere 9.9 days of rain per month.
Sending you warm wishes
Sdack
It been a long time since I was in that area, but I can remember you are right....
here is a bit of math involved.
fyi a sun hour is 1 hour of maximum sunlight per m2 for your area, at the equator it is 1000watt/m2, you are probably up at 800-900watt/m2 in summer, don't know about your upcoming winter maybe 700watt/m2.
If bleak days deliver 250watt/m2 per hour that would mean you need 4 hours of daylight to have one sun hour.
If the panel is not in a 90 degree angle with the sun the surface collects less sun dropping the amount of light per m2 of panel surface(and this is a fact for most hours of the day).
Per degree temp rise your panel will also produce less energy, about 0.5%
Is this understandable for you?
It's not about those sunny days, if you have 8-10 sun hours, lets say your 50watt panel deliveres 300watt a day on these days
your suggested batterie is 480watt.
In the morning (let's say after 16 hours of draining and that is longer than in actual life) you have 16x8=128watt used, the panel charges that in 3 hours, leaving the rest as unused, just to compensate batterie discharge and the 8 watt/hour for your rig until sun goes down and panel stops charging.
Now you have a poor, clouded day, about 1/2 sun hours, it's colder so let's say it gives still 20watt, that mean your batterie is discharged by 172 watt a day.
this setup would then run 2-3 of these days before your batterie is completely flat and you wished you would have arrived earlyer.
You can probably find info of average sun hours for your region to make an good estimate what is needed.
You could use a li-ion pack of f.i. an electric bike to take along on those cloudy days to charge the batterie if voltage is getting low.
And I thought my setup was bulky......with only 2.5watt/hour drain.
what camera do you use for your setup?