David, VHB tape works great for flexible panels, and it is pretty good for panels mounted front-to-back on the larger "front" shell. But on the rear shell, you probably have to mount that panel side-to-side. The outside of the rear shell has a lot of curvature, both from the center ridge (towards street and curb sides) and from the higher "seal" in the middle going down towards the rear. Those curves make it difficult for panel mount Z-bars to make good contact.
The "flat bottoms" of those Z brackets are typically about 4 inches long, one inch across. You can bend the one-inch side pretty easily, creating an angle different than 90 degrees, but bending the longer length is nearly impossible. You can't match the curvature of the shell roof, and the gaps create a problem in trying to use VHB tape.
I have a solid-framed glass panel back there, it's very similar to yours. I built a curve into bracket bottoms by using VHB tape segments of of different thickness. After pushing the panel and brackets down into the rear shell roof, I also applied 3M boat sealant around the bracket edges to further strengthen and weather-proof those attachements.
But that took too much time, and it is weak. A far better scheme would be to use 2 bolts on each Z bracket. On the outside, after drilling holes for the bolts, fill the holes with boat sealant before tightening the bolt through the roof. The inside ceiling should have a big "fender" washer above the nut, you might add another washer outside too. When you push the bolt into the hole and begin tightening against the nut and washer inside, boat sealant will fill into the bolt threads and also leak out under the washers - making a great seal, very strong and waterproof. Just wipe away any excess. I would use SS bolts and washers, because aluminum is too weak.
