OK I need to know how to get my marshmallow fondant to not dry out. It rolled out quite nice, was great to work with etc. but after I did my cake sign (a piece of fondant that i wrote Happy Birthday on) and it sat out for a couple of days, it got dry and was cracking. How do I prevent this?

The first thing that comes to mind is perhaps to grease your hands and work surface using Crisco when you knead and shape the fondant. While I've never personally experienced a problem with cracking for the small items I've left out to dry made out of fondant, Crisco, unlike water, would not evaporate over time. Just greasing your hands/counter with it will work some of it into the fondant.

I also work some crisco into the fondant itself. Works out very nice.