How much storage?

[Qxxx]

I suppose it would be a problem if you had a solar panel on your roof.

I've seen people do it where they have the carrier on one side and the solar panels on the other side. 

Back when I had my Cherokee, and I roamed around the west for a year and 1/2, I had a full-sized Yakima cartop carrier. Inside I kept the dome tent, a good sized folding lounge chair. and a lot of other camping items.

 

[Tony's Dream]

My van is a Ford Intransit cargo van, so space is premium. I built in an expanding bed and a fixed cabinet on the opposite side. To maximize my space, I went with cargo netting that hangs on the sides and roof. This frees up floor space and the nets are flexible so you don't get the closed in feeling.