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I once made a large (24") diameter tube for a 20" newtonian. I used cardboard tubing (about 10 mm thick) on which I put on the ouitside a single layer of fibreglass matt and resin. On the inside, I also put a layer at each ends but only for about 200 mm up the tube. The rest of the inside I just varnished with epoxy resin and then painted matt-black. I didn't vacuum bag it or anything like that.
To finish the outside, I coated it with two coats of white-gellcoat. For the first coat, I used a roller and this gave it a sort of stippled finish. I then sanded it and gave a second coat with lots of styrene wax in it which gave it a very smooth (but still stippled) and tough surface.
This tube was very stiff and there was no need for carbon or kevlar.
For my 10", I wanted to do the same (but with carbon fibre and vacuum bag it to make it lighter) but I couldn't find any 12" cardboard tubing - the place that I got the 24" had closed down and I was unable to find anywhere else in Perth that sold large diameter light-weight cardboard tube.
So as a result, I made a mould using PVC stormwater pipe and then used the mould to make a tube with a smooth ouside.
It took a long time and a lot of extra cost - first sand and polish the PVC, then make a two-piece mould, polish that, then the tube.
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