I also managed to mould a carbon spinnaker hoop on some 32mm silicon tubing.
I filled the tubing with Hayling's finest sand, covered with carbon sock and epoxy and then formed to shape and consolidated with electrical heat shrink tubing.
I should have used slow hardener as the resin was setting quicker than the heat shrink was collapsing so it is not perfect, however I don't have slow hardener.
The silicone does not stick to the epoxy however it would not come out until I had worked some fairy liquid in.