I spent some time talking solar panels with a rep from Goal Zero at a outdoor expo here in SLC last weekend, a seemingly great product with some neat applications. Hiking, backpacking, emergency preparedness, hunting, fishing, etc all come to mind but I don't gather they have much application nor do they imply much application for vehicle based travel. Now I realize there is a fundamental difference between a user that moves on a daily basis or at least a few days a week and someone that sets up base camp in the same location for 3+ days. But as has been eluded to if your really interested in solar powering 12V accessories normally tasked to your vehicles charging system (ie fridges, high draw lights, stereos, etc) then you'll need far more wattage and surface area than a smaller panel can accommodate. For my travel routine, its rare that we are parked for more than 2-3 days and my single batter covers those needs including 24 hour fridge use (cycling as needed) and a low draw LED light at night. Worst case I have an isolated (when key off) 2nd battery that will reliable protect my start abilities. So while it is a total tangent from solar recommendations I would urge you to investigate a quality dual battery system before you opt for an arguably more troublesome and time consuming option ie solar.
I'm planning a Utah converse moto trip that will have us on the dirt for ~900 miles across some of the most remotes areas of Utah. My bike has lights but not enough power to readily run even some small accessories ie a phone charger, GPS & aprs tracking system simultaneously. It can handle some but not all... here is a seemingly appropriate application for the smaller Brunton/Goal Zero type solar kits. If I could reliably charge my GPS batteries during the downtime, or possibly capture some light during the day?