The best thimble to use is the closed end "sailmakers" thimbles. The biggest problem I have had with the synthetic lines around standard thimbles is that they do get abraded around the sharp V. You actually don't need the thimbles at the top. They are necessary at the bottom though depending on how you run the trap line to the hook through them. I have made about 6 sets or so for boats that I was able to keep an eye on and there have been no issues except on the boat with the 7/64 amsteel and a 240lb dude hanging from them who likes to fly around the forestay on a routine basis. Those abraded relatively quick. Another boat has had them up in the Florida sun over the summer and there were no problems.

and they are eyesplices around the thimbles. I would recommend 1/8 because it gives you more play room before the abrasion becomes a problem. Our Scandinavian friend uses knots and hasn't had a problem. I like splicing them so I do that.