Preheat oven to 350 degrees. Cream together margarine, shortening and sugar. Add eggs, one at a time, beating after each. Sift together cocoa, flour, and soda. Add to creamed mixture, mixing thoroughly. Combine tomato juice, hot water, and marshmallows; add to batter. Add vanilla. Batter will be thin and marshmallows will come to the top. Pour into 15 1/2 x 10 1/2 x 1 inch pan. Bake for 35 minutes. Ice while hot.