I converted a roller trailer to bunks for my SIB a couple of years ago, basically doing what you are suggesting (I used astroturf rather than carpet but both can have friction issues so be a little careful here).
I also made some smaller blocks that sit underneath the boat to that the boat does not sag....for want of a better technical term! It took a bit of fiddling about to get the heights etc. adjusted so that the trailer fitted the boat. I went over to see the guys at De Graaff trailers (https://www.degraafftrailers.co.uk/i...-boat-trailers
) who were really helpful in advising and selling the brackets and metalware etc.
Best of luck...a few hours on this will save you loads of time when launching and retrieving your boat (more time on the water!!!!)