Create a Floating Moon Answered

Hi there,

i need help, It's almost my wedding aniversary, and me and my wife have this agreement that we gonna surprise each other every year, well there is one thing that i'm doing this year, been thinking about it since we got married, but never got the gear to do it, well now it's diferent, there's only one thing left, i'm going to steel the moon for her (a moon done in machê paper) theres only one thing, what can i put inside it to make it float?
I've tought about making it with a beach ball filled with helium but it seems that the ball leaks, does anybody have any idea????

Glad for the Help,

Nuno