I don't quite understand your logic. I don't think you flipped your Jeep on the dunes because it was too light, but more due to driver error. With that being said.....
I ran a 'glass bodied CJ7 for a while. The grounding issue really isn't a big deal. I had copper plate which sandwiched my tub using three studs. My dash harness was grounded to one stud. Stud #2 went to the engine block. Stud #3 went to the frame. Kinda redundant, but I didn't have electric problems.
I think 'glass is fine for trail-ridin', but it doesn't accept impact forces too well.
I don't have any experience with Kevlar tubs.
On my next project, I'm trying to decide between repairing steel body, or just ponying up some loot for one of these products.
http://www.aqualu.com/CJ.html Stronger than steel, light as 'glass, no rust...