Measure sliced bananas into a large bowl. Beat on low speed of mixer until bananas are mashed. Add cake mix, water, eggs, and rum. Beat 2 minutes at medium speed on mixer, or as directed on package. Spoon into a greased and floured 13 x 9 pan. Bake in a preheated 350-degree oven for 40 to 45 minutes. Cool.
Combine egg white, brown sugar and water in the top of a double boiler. Place over boiling water and beat with mixer until light and fluffy. Spread on the cooled cake in pan. Decorate with banana slices and cherries.