As you're intending to replicate the inner.skin as well and bond both panels together, this will provide support.and stiffness to the whole part. 

If lightness is important, then a 240g surface twill (looks and handles much better) backed with a 650g backing will work well. Some additional local reinforcement around fixing points would be a good idea, plus some around the outer.lip if the support skin doesn't extend right to the edge.

Going down the Soric route will give you a very rigid panel, but you'll get a very noticeable hexagon-contoured print at the surface and possibily a little more weight from the resin uptake. I don't think I'd use it personally, unless it was a single skin structiure but you.can always re-make if you're not happy with the results?