I'm hosting a baby shower for a friend having twins. I was going with the "2 peas in a pod" theme and wanted to make some cake balls (we'll see since attempt 1 was a bust ) and put them inside fondant peapods. Would fondant dry firm enough to make an open top peapod? Would I need to mix it with gumpaste?

It will dry, it just takes longer without gumpaste.

I agree fondant will dry, but it does take longer. I would personally make it out of either a mixture of both, or even all gumpaste, and let it get good and dry. I'm no expert though.

If your fondant is too soft, the balls may lose their shape and be flat on one side. Try either fondant & tylose, or fondant & gumpaste mixture.

I like the 50/50 gumpaste/fondant mix.