I haven't had any issues with marks or indentations being left on the hardtop. One reason is the rubber trim stips on the cart. I think the lighter weight of the hardtop combined with the low-pile headliner helps as well
So the Mabett roof rack extension only works on the rear most hardtop slots (4dr) and wont fit the front slots? I too wanted to just purchase two extensions for the rear hardtop
Now if @IAG Performance (or another wiring manufacturer) could manufacture a pigtail that plugs into the center rear interior light with a wire to run up the drivers front to connect to the IAG harness, that would be ideal. I would purchase one and I'm sure a lot of other IAG customers would as...
Assembly was fine, just tedious with one person. Definitely read the particulars on the PDF as well as watching the video. I had to disassemble a few sections to reposition items I would have caught had I paid closer attention