I was wondering how long RKT will keep? I am going to make some building blocks (fondant covered) for a cake and I would like to make these a week or two ahead of the event. My concern is will the RKT go soggy and/or loose its shape? And what should I use to help the fondant stick? Royal icing or buttercream? I don't think the blocks will be eaten if that makes any difference...

I'm pretty sure they would harden over time. I would use buttercream to use as "glue".

If they're completely covered a week shouldn't be a problem. I always cover mine with buttercream and then fondant.

Thank you!
I guess I'll better get started then