Kevin, I love your McGyvering. Brilliant.
I have used both PL Premium and Pl 400 in my Egg, with superb results. Once that stuff sets up, it will pull glass fiber chunks out of the shell if you try to remove what you glued on. I think the physics are first that of cohesion, followed by both cohesion and adhesion. It's tough stuff.
The brackets are lovely. I'm going exactly the same route to attach window valances and roller curtain rods to the inside, just cutting a square out of the Ensolite to accommodate the attachment. I truly believe that glassing the blocks wont be necessary, especially for light
Where did you obtain the EZ-lock stuff?