I was informed last week about this issue, it was my first time also.
1.- Buy PRE MADE RICEKRISPIES BARS, best advice ever!
nuke it for 5-10 seconds.I forgot about this step and it almost cost me, but I manage it to fixed it
2.-Not to make it so much ahead of time because it becomes stale, it does not matter if no one is going to eat it
Don't count on it! Everyone is going to try to get a piece of it, if not the whole piece
3.-Covered it with modeling chocolate...I did not have that so I use Wiltons candy melts...BIG MISTAKE!! I ended covering it with buttercream on top of the candy melts plus the fondant on top, the neck of the guitar was a bit thicker than I wanted . When the kids found out the neck of guitar was made of RKP they could not wait for the cutting of cake. I was making a FLYING V GUITAR CAKE,
I wished you luck!!!!
I learned all of this thanks to all our CC friends here.