You got two real booger places for stripped wood screw threads. The jackplate is in the endgrain of the body and it hates threaded fasteners. If the wood left in the hole looks like a powdery mess, go with Nalo's fix of good wood glue and as many toothpicks as you can stuff in there. Let dry for 2 days. 2 days. 2 days. As for the cavity cover, go for longer screws. Did I mention, let the glue for 2 days?