terryaGJ wrote:
I might have to rethink this.
An alternative might be to mount them on the sides. There is a member on the Forums, Tom from New Hope, that his modules on the sides. He has a hinge apparatus that allows the modules to be flat or at any angle. A strut is used to prop them up, IIRC. The hinge pins are removable so they can be deployed onto the ground, if necessary.
If it was me and I couldn't find the roof truss under the plywood (I can and did), I'd use a molly bolt just slightly smaller than the bracket hole and through drill the roof, insert bolt, tighten, and they are fastened. Cover the bracket with your sealant of choice.
FWIW, I installed my mounting brackets through a layer of Eternabond tape. This 45 second
Video at Eternabond convinced me.