I'm using stabilized whipped cream for this recipe because it will soften at the same rate as the ice cream filling. Any type of whipped-topping like CoolWhip or Bettercreme is going to work well. If you're traveling a long distance with your cake, use a more stable buttercream like easy buttercream or American buttercream. Then store the cake in a cooler with dry ice to keep everything from melting, especially during warmer weather.