I wouldn't freeze it at all. As long as you keep it in a cool dry place and cover it to keep any dust off it, it should be fine for a couple or three weeks.
I've never frozen RKT, but if you feel you must freeze it, You should wrap it well in plastic wrap, then a layer of foil. When you thaw it, you probably should leave it wrapped till its completely thawed so as to keep any condensation off of the RKTitself. In other words, treat it the same as you would a frozen cake.
I have kept sculpted RKT pieces for weeks just wrapped in Saran Wrap and left at room temperature. I'm sure they may get a little stale (I think they would if frozen, too), but they don't spoil. I'd be a little leery of freezing them.
In the interests of copyright law and other such, I usually refer to my rice sculpting material as Rice Cereal Treats (RCT). Its also closer to the truth because I generally use the generic rice cereal rather than the name brand.