I did the carpet on my old TriStar. I was able to remove the old carpet pretty much intact in sections and used that as a template for cutting the new pieces. As has been mentioned, doing it in a warm place is important -- hot sun even better! -- so that the carpet can conform to the contours. Measure twice, cut once.
2005 X2, Viper Red, MCX, OJ TZ-X5 prop, PPass, rear 750 sacs, KGB, IBS, Bennett Wake Plate, custom wake shaper
(previous) 2001 X5, 1991 TriStar 190