You could maybe install a set of aviaton skylights. Usually found in a variety of small high-wing aircraft, they look like two parallel enlongated ovals and are available in clear and a variety of tints. Here's a LINK to one vendor that sells skylights for all different kinds of aircraft. Unfortunately they don't have pics but I imagine you could request some and dimensions. Since they're suitable for mounting in aluminum sheet they should work nicely in the VX roof.