You need to make it strong but try not to go overboard with a lot of epoxy making it really tail heavy. Try and use CA where you can and epoxy the triangle stock on. I don't remember how these came out of the box (tail, nose heavy or neutral) but you can always move the battery forward to compensate or put on a bigger engine!
Oh and if there are rough spots, pot holes.divots, in the balsa after repair get a small container of lightweight spackling compound , fill in the dents and sand smooth . Then you can cover the sins with a piece of coating or paint it.