I like the concept, but to look clean the top of solar panel should be flush or slightly below the top of trunk; that means, hacking away on an oem trunk. That presents sealing design issues though, for water, but can be done.
I wouldn't call it hack, but do call it crude looking. Idea is solid, but to do it right, see above.
Another thing I would use it for is a fan to circulate air in the interior, but that would be a direct wiring (so if you can dedicate certain cell rows (?)) and only with the sun is out, to avoid battery consumption.