I never found layaing fiberglass on the inside of a hull difficult. I usually lay a 3 inch wide strip of bias cut glass along the keel (inside) for extra strenth, let it cure and sand smooth slightly, and then lay the whole inside of the hull with cloth. The inside is smooth and looks nice.

I also agree with another response that pre-glassing the panels before stitching up could make the panels more difficult to bend into shape. For example, I wouldn't recommend it on my Point Bennett design, because towards the stern, there's enough twisting going on with the bottom panels. Glassing before stitching would just add that much more pressure against shaping the hull.