When I did the surco on my bronco, I got some thin aluminum stock from Lowe's, and used a solid piece for each side. I then drilled extra holes on each rail. Windshield sealant in each hole, silicon under the rail+ between the aluminum and fiberglass, then silicone all around the outside+bolt holes of the rail and aluminum. I had no leaks, and no problems with cracking. I was comfortable putting 125lbs plus the weight of the rack up there.
Do you have any pics of it on the jeep? I'm wanting to get a hartop and reuse my surco rack on it.
Today: I removed the cheap multiple hole trailer pin sway bar disco's. Got a hex head bolt the same size as the stock end link bolt, and a wing nut. Tightened everything, marked the bolt, drilled it out, and put a pin in to keep the wing nut from backing out. Guess what, my jeep is clunk free. Well for now...and the front feels a little tighter on the highway