-We put in 'plus nuts', a beefier version of rivnuts. They required a 3/8" hole. I put 2 bolts in each 'wing', just a bit inboard of the outer round tubing, in a couple of round cross members. I don't think the wings extend far enough to put them in the outer framing.
-Hard to see the bolts heads
-The SSS plates have more coverage, including protecting the bottom of the fuel tank (which has its own thin layer) under the passenger seat. Just went and looked at KG's buggy; the fuel tank 'skid plate' support bracket is bent, mine are still straight.
Like anything else, pick your poison.
Also, a good idea to use a paddle bit or similar to drill a recession in the material for the washer, bolt head.
I didn't think of this at the time . . .