Solar panel powered aux battery

Has anyone had the idea or tried to build a solar powered auxiliary battery for a survival setup? I ammlooking to build a small battery hookup in my bed for car camping.

 

I have a setup similar to what you want. I have an aux battery in my tool box in the bed but I have it hooked up to the alternator with an isolator. But I also have an input in the bed for a folding solar panel I made. I'll get some pics

 

I have a solar panel (160 watts purchased on sale from Solarblvd.com) mounted to my Yakima rails between two bike racks. It feeds a marine battery in the storage drawers in my bed which powers a refrigerator, water system, and auxiliary outlets. It's far more watts than I need but it was a good price and I can fully charge my battery in just a few good hours of sun and it's efficient enough that it will still work in dim light.