For the cake: In a medium bowl, combine the raisins and rum. Let soak until the raisins absorb the rum and become plump, about 30 minutes.
Preheat the oven to 350 degrees F. Spray a 9-by-13-inch baking dish with nonstick cooking spray.
Mix the cake batter according to the package instructions. Drain the raisins and fold them into the batter with the walnuts and coconut. Pour into the prepared baking dish and bake according to the package instructions. Let cool completely.
For the filling: Meanwhile, prepare the pudding according to the package instructions; refrigerate until chilled.
Combine the heavy cream, sugar and vanilla in a large chilled bowl. Whip with a hand mixer or whisk until medium peaks form.
Fold the whipped cream cheese into the prepared pudding. Fold the whipped cream into the pudding and cream cheese mixture. Refrigerate until using.
For the garnish: Line a baking sheet with parchment paper. Melt the melting wafers according to the package instructions.
Dip each strawberry into the melted candy all the way up to the green stem, covering all of the red of the strawberry. Let the excess drip off, then place on the prepared baking sheet. Let sit until the coating has hardened. Using a toothpick or skewer, mark lines across each covered strawberry to mimic the ribbed lines on a carrot.
To assemble: Carefully remove the cake from the pan and place on a cutting board. Cut the cake into 1-inch cubes.
Place a third of the cake cubes in an even layer in the bottom of a 3-quart trifle bowl. Top with a third of the filling. Repeat to make 2 more layers of cake and filling. Mix together the crushed gingersnap cookies and graham crackers and sprinkle over the top of the trifle. Arrange the dipped strawberries on top to mimic a carrot garden.
If serving to children, you can omit soaking the raisins in rum.