The only gum paste I use is the Wilton's premade stuff. Since gum paste is not really made to be eaten (though it is edible...it tastes like bleh), I don't spend a lot of money on it. I use the 40% off coupon you can usually find at Michaels or Hobby Lobby. I have never had a wilting problem with an item if it is completely dry. But then I've never kept them very long on a cake in the fridge.
There is no reason to refrigerate your gum paste flowers or figures. Make them well in advance and keep them covered (away from bright direct light --especially fluorescents if you are using bright colors). Once a gum paste item has dried it is light and very hard and they keep forever.
Becauses colored gum paste can dry lighter than say fondant or your buttercream, I will go over them with a mix of lemon extract and gel color to deepen and match any colors that need to be matched. (Had to do that with a purple ball cap brim to match the purple buttercream).
Anyway, that's my Gum paste 101 crash course. Love the stuff. Oh...and that tip about keeping them in your oven with just the light on does work...just make sure your husband doesn't come in behind you and turn the oven on to 350! Not pretty!