I had the same results as you, so I gave up too. I use Satin Ice now. It is more expensive, but saves me hours of work and labor, and it is consistent. I personally didn't like the MMF, it seems to be too stretchy for me.
I don't know how it will hold up after applied to the cake and frozen, but I freeze my whipped Pastry Pride all the time. It hold up really well, but I find it does need a little re-whipping to get the firm consistency after being frozen. It seems to deflate some after being frozen and needs a little help.
I have made a few cakes with flames, my husband is a firefighter. Here are the links to mine. HTHhttp://cakecentral.com/gallery/1654741/let-it-burnhttp://cakecentral.com/gallery/1626419/32-years-of-service-earns-you-a-lifetime-of-corona-on-the-beachhttp://cakecentral.com/gallery/1973651/coming-full-circle