I have not, but it sounds easy enough. I would probably used an aluminum backer plate as opposed to just a fender washer. Maybe a 3" to 4" round or square piece under each bolt. 3/16" or 1/4" thick. The thinking would be that you (or someone) might start using it for something a little heavier in the future. I'd rather overbuild than underbuild. The further away from where the top mounts to the aluminum structure, the more reinforcing I would do. Given that most handrails are SS, as well as the bolts, it might not be a bad idea to use SS backers. It would save an extra step of having to isolate the SS bolt from the aluminum backer.
A couple of ideas to get the creative juices flowing... if you used a 1" rail, you could also mount racks like you see on top of car roofs (Yakima, Thule). It would give you further options down the road with the ability to mount bike racks or safari racks, etc. If you only wanted to use the hardtop for beanbags, then maybe you only needs to install eyebolts?
