Four angle brackets worked well for this solar install I did on a friends van. We found the four nearly perfect spots on the roof. 3M 5200 sealant / adhesive for bedding, and through bolted with backing plate. Lowest profile I could get. Also installed the two MaxAir fans. But as Rob said, these type of tops have contours in all directions!
Beastie 3: 2002 7.3 EB Cargo: Agile TTB, CCV Mid Top, Custom Walk Through, Lots of stuff added. BlingMyRig.com