At the risk of being the single voice of dissent, papering and glassing in unnecessary.
NAR competitors have been flying the Dual Egglofter competitions for over 40 years. You need look no further than published plans for US record holding Dual Eggloft designs to see what kind of materials they used. I did a very cursory search and found one design that used 1/16" plywood and another that used 1/8" balsa. No reenforcing was required for either. The design employing balsa used a low aspect ratio fin shape as I suggested above.
You may want to do a more thorough search for designs than I did, to see what other materials choices folks have made for this event. But I suspect you see more of the same. After all, these are LOW POWER rockets, with a less-than-optimal frontal area, carrying a massive payload relative to the motor's peak thrust. These vehicles are not attaining the velocities of sleek 4FNC high power rockets and therefore not experiencing the same level of aerodynamic stress.
