Leaving the flared tube and glue/mandrel issues to one side for the moment, if you are using a roughing gouge Miles, as many folk do, myself included, I would suggest your tool presentation is a major contributor here. Roughing a log is one thing, but roughing and shaping a pen barrel requires you to use the bevel just as you would a spindle gouge or a bowl gouge.
Judging by the amount of tearout you are showing, my guess is that you are presenting the roughing gouge front on, with the flute pointing upwards, and at a fairly horizontal angle, which is serving to scrape the wood rather that sheer it. Try turning your gouge so that the flute points to about 10 o'clock, lower the handle so its about 10 o'clock to 4 o'clock (adjust your tool rest so that you are still cutting at or just above the centre line of the wood, using the lower wing of the tool) and when viewed from above, present the gouge at about a 45 degree angle to the work (assuming your bevel is at 45 degrees). That way, you will be rubbing the bevel - and the tool, assuming it is nice and sharp, will behave like a skew.
The difference in the surface you are left with will be remarkable, and you will be much, much less susceptible to disaster.
