As you correctly state, you have a rolling brick. Add solar panels to it and its still a rolling brick.
Add a deck and solar panels and then you just have a bigger rolling brick with sharper edges.
BTW: did I mention its a brick?
Cowl or aerodynamics not needed, and likely not noticable, but hey, if you ever get the itch, it's a place you might get back a fraction of an MPG, and if you do a lot of driving it could be worth it!