Bake the cake according to package instructions using the eggs and vegetable oil for the cake.
While the cake is baking, make the caramel sauce. In a saucepan, whisk together the evaporated milk, sugar and eggs. Add the butter and put the pan over medium heat. Cook, stirring constantly, until the mixture thickens and just starts to bubble, about 10 to 12 minutes. Remove from the heat and cool completely. This can be made a day ahead and refrigerated once cooled. Bring to room temperature when you are ready to use it.
To assemble the trifle in a large trifle bowl: Cut the cake into 1 1/2-inch cubes. Make a layer in the bottom of the dish with 1/3 of the cubes. Drizzle with some of the caramel sauce, enough to moisten the cake but not cover it completely. Sprinkle with 1/3 of the coconut and 1/3 of the nuts. Repeat twice more adding a little extra drizzle of caramel over the final coconut and nuts. (Any extra caramel sauce can be used as a topping for ice cream or pound cake.) Serve immediately or refrigerate until you are ready to serve.
Cook's Note: the trifle can also be assembled in individual wine glasses or large tumblers.