I use a carbon sleeve. Don't know if it's really better because I used it from the start. But it's at least more convenient than the o-rings and it's cheap.
My impression is that the carbon fiber sleeve is intended to be used with the barrel bushings (barrel rings) The carbon fiber stiffens the barrel, and the rings center the barrel in the shroud Takena look at the 2 items below from Cape Fear Airguns, and see what you think
FX Superlight Barrel Bushing Specially designed spacer to allow a FX Superlight barrel the ability to use a carbon fiber liner sleeve (3 spacers / pack) Models: Crown or Dreamline Fits all calibers if installed with the appropriate caliber CF sleeve. Fits all barrel lengths.
Carbon Fiber Liner Sleeve tested by Ernest Rowe and myself, has now become an official FX Airguns Accessory! It is designed to fit over your STX liner, replacing the support O-rings, to provide a new level of stability, rigidity, and harmonics to your STX barrel. Get the FX Carbon Fiber Sleeves...