AI'm wanting to make some cupcake toppers ahead of time and needing them to stay moist/soft and not dry out. What is the best way to do this? Would placing them in Tupperware be the best way?

AYes, an airtight container should do the trick. Or in a sealed plastic bag.

My I ask why you wouldn't want them dry?

They will continue to pick up moisture from the icing when you put them on and you could end up with a disaster on your hands.

Just a thought....

When I have fondant pieces that I need to keep flexible, I like to place them on cheap plastic chopping mats in a zip lock plastic bag. 

If it's going to be a few days, I dampen a small piece of paper towel and place it between the bottom mat and the bag.