Solar panels on a truck?

I took my family to the LA Auto Show yesterday. Despite studies and articles contending that young people today are not so attached to automobiles, my son is absolutely captivated by them. He knows the makes and models, what he'd like, how he'd modify it, etc. I knew he'd have a great time and he did. I wanted to see developments in electric vehicles, plug-in hybrids (PHEV), etc., both production and concept.

I noted a pickup truck with a tonneau cover consisting of a solar panel and wondered about its practicality. Neither the Via Vtrux pickup (a series PHEV) nor the SolTrux panel option are in production, which is anticipated for 2014. It's a nice looking truck.

But is the solar panel practical? I have a Jeep pickup into which I've installed a 32 gallon water tank and other items designed to let me be self-sustaining in the Mojave, Sonoran, and Great Basin deserts of the Southwest. Where better to capture the sun?

So what are the appropriate numbers? We'd like to have battery capacity, dimensions and efficiency of the solar panels, and the claimed output. Here we find that the battery pack is 22 kWh. The dimensions of the panel array aren't given. but the standard bed is 78.7" long. The width isn't given but might be 65". The larger panel is stated to be 800 watts.

I see here that, in March (about average) I can expect on the order of 5 kWh/(m^-2*day) (kilowatt hours per square meter per day) for a panel mounted horizontally as it would be on a tonneau cover or roof rack. If I assume that the panels are 72" X 60", or 2.8 m^2 they should intercept 2.8*5 14 kWh per day. At 20% efficiency, I should get (surprise) 2.8 kWh/day. Assuming that I'd never let the battery pack below 20% charge, it would take 17.6/2.8 or a bit over 6 days to fully charge the battery. And the 22 kWh is represented to be good for 35 miles (though my desert miles are VERY hard on energy use). At that ratio, a day's worth of sunshine would take me (2.8/17.6)*35 or about 6 miles and probably a lot less in the rugged terrain where I'd be operating.

I suppose that, were I (through incredible stupidity or possibly a punctured fuel tank) out of gas and stranded, I could drive six miles per day for however many days it took to get to civilization (a very long way from the places I go). The fact of the matter is that it simply takes a lot of square meters to provide significant power. Verdict? NOT worth the estimated $3,000 price for the panels.

Update: Here's a clickable link to the article cited in the comments by Anonymous.