Our tarc team has made their own carbon fiber tubes for the past couple of years. the commercial tubes aren't the right size and are too beefy. They use a coupler tube from Balsa Machining Services as a mandrel. The mandrel is first fitted with a layer of mylar, which acts as a release layer. It is sprayed with frecote before the lay-up begins. Once it is layed up, a layer of peel ply is added (very important step). We use 1k fabric from SollerComposites and do 3 wraps. It's not strong enough for HPR, but it's definitely strong enough for TARC and super light weight. Here's a pic of this year's first rocket, BT60 and a 29mm motor mount. This is a lot of work though.