Solar iPod dock charger

Hi forum, I'm a bit of a n00b in the electronics department so i've come here for help.

I'm wanting to make a solar charger for my iPod doc so I can take it to Glastonbury Festival. I'd like to be able to play music at my tent without having to lug loads of batteries from my car.
My dock already charges my iPhone and is rechargeable itself so I only need to provide power for the dock to keep the whole lot going.
I've looked at some videos on YouTube and from what I can make out I need solar panel/s and a voltage regulator.
My doc is usually powered via an adapter which outputs at 12.9 volts.
My 1st question is what voltage regulator do I need? 12V, 12.9V or 13V? (I'm not sure if they come in these specific voltages).
My second question is ideally what voltage output solar panels will I need to run something like this?
And my last question (for now) is it completely unrealistic to power something like this off of a portable solar panel?

Thanks

Anyone?

We do not know what the battery chemistry is: Lead-acid, Ni-Cad, Ni-MH or Lithium.
We also do not know what the battery voltage is.
We also do not know if the charger circuit for its battery is inside the doc or if it is inside the adapter.