Oh,
what you are looking at are 3 SUPB (Stand up paddle boards) , brought these up from Vancouver to Whitehorse for a friend of ours. How they are secured is quite simple. Using shaped foam blocks, these are placed outside on the soft top, directly above the rear roll cage member that supports the top, thus, there is no pressure on the top at all. Then i have a run a compression strap around the boards to the large tie down rings at the back of the G, I don't know if the civilian version has these or not, they are used for slinging or tie downs to rail cars.
What I'd like to get is a custom hard top, but just the roof section, and run soft sides that I can remove, that would be the ideal set up for us I think!