Pulling three or four strands of 12 gauge wire through 200 feet of 1/2" CPVC doesn't sound like an easy way to go.
As stated in other posts, the neutral needs to be the same size as the hot conductor. This is true even if you go with four conductors (2 hot, 1 nuetral, 1 ground). That's because it carries the same current if only one leg is in use. (If the current is balanced between the two legs, then there is zero current in the neutral. But that's seldom the case.) Also, the ground is normally the same size as the other conductors to ensure that it can carry enough current to fault the breakers.
By far the simplest solution is UF, sized appropriately. From your earlier post, it seems unlikely you'll pull more than about 15 amps, and it's all resistive load. I think you could get by with AWG 10, fused for 20 amps. If you're thinking of going to AWG 8, consider running four conductors of AWG 10 and use a 240 volt heater; it might be cheaper in the long run. You'll need a subpanel in the hut if you go that route.