I assume you're using Sweetex and pouring fondant. Why is that? Isn't that a little expensive? What is the problem you are having with the buttercream.....is it too soupy? Why not use powdered sugar.....is that not kosher?
Here is a Sweetex buttercream recipe. The meringue powder is optional.
Sweetex Frosting
1 tsp vanilla extract
1/2 tsp butter flavor
1/4 tsp almond flavor
1/2 cup water
1 1/2 cups Sweetex
1 TBS meringue powder (optional)
1/2 tsp popcorn salt (or regular salt)
2 lbs. powdered sugar
Add salt, vanilla, butter, and almond flavors to measuring cup. Add cold water to make 1/2 cup.
Beat Sweetex and slowly add water until fully incorporated. Beat in meringue powder. Gradually add powdered sugar. Beat 2 minutes at medium speed.
This recipe is in its original form….however….*I* don’t use popcorn salt, just regular table salt. Popcorn salt is finer ground so I guess it would dissolve better, but I find regular salt is just fine. Just make sure to stir until dissolved.
Also, I have made this with AND without the meringue powder. I found no difference. I think the meringue powder is supposed to make the frosting stand up better in heat and humidity.