Make cake based on directions found on the box for 9" round pans. Make 4 pans of cake. Remove from pans and place in freezer, wrapped in plastic until frozen. Make whipped cream. Remove frozen cakes from freezer and place one on a plate. Spread strawberry pie filling on top, and place the next layer on the cake. Spread the filling on that, and the next layer on that. When all four layers are in place, spread the whipped cream all over the outside of the cake.