Bake in 2 (9 inch) layer cake pans according to package directions. When cool slice each layer in two (4 layers).
Mix strawberries with 1 carton Dream Whip. Spread half the mixture on one cake layer. Add second cake layer, spread with custard filling, add third cake spread with remaining strawberry mixture. Add top cake layer. Frost entire cake with remaining carton Dream Whip. Refrigerate overnight.