I have always just used plain, sweetened cream. Use confectioners sugar to sweeten it, and use the heavy-est and least pasteurized cream you can find. If you need something thicker, you could go with a cream cheese frosting instead. Lots of bakeries use stuff that really isn't real cream for their frostings. Also, trying to use the stuff in the can ( like ReddiWhip) won't work. Even if you use the one that is real cream, it just dissolves in a matter of time.