Fred,
One way to make carbon tubes that is pretty fast is to use a male mold (mandrel). In your case it could be the old aluminum beam that has been stripped of fittings with any holes filled up. Can also make one out of solid wood. After using your favorite mold release wet out all the unidirectional you plan to use on the mandrel and wrap the outside with a layer of Dacron peel ply tape. Next, wrap the wet uni with two layers of polyester heat shrink tape. This is available from Dunstone Industries – they recently added a store front to their website. The polyester can be shrunk with a hair dryer or heat gun and applies a lot of compression to the lay up. Resulting laminate is good quality. Use an abrasive cut off wheel to cut the cured carbon lengthwise so the tube can be pulled off the mandrel in two halves. Glue the two haves back together along the seams. Step two is to remove the peel ply and wet out your carbon cloth around the outside of the carbon uni tube. Repeat the shrink tape routine minus the peel ply. Sounds labor intensive but really it goes pretty quick. The polyester tape leaves a shiny finish surface on the outside that needs little sanding. As someone else mentioned, you need to locally reinforce any holes for fittings or fasteners with extra layers of cloth.

Kevin