I would only buy the bunks, but good bunks. I had a King Trailer I bought for my last boat. The bunk slicks on those trailers are one piece and are very slick. Don't pull the front strap off until the boat is in the water. I am not sure if you can buy those exact slicks as they go over a 2x. They are like having rollers.

My buddy's trailer has to have all of the rollers replaced and it is pretty expensive. He is not very happy about the price. There are a ton of rollers on a roller trailer and they are not cheap.