I have a waterproof bag that came with my diaper bag (a Land's End one, love it) that I keep wet/dirty diapers in. I've never had an issue with smell when the wet bag is sealed inside the zipped up diaper bag, even with some of DS's toddler poops! Check out some diapering sites for a good wet bag, or heck, I've used a ziploc in a pinch. As long as it's sealed inside something and inside the diaper bag, you should be fine. You can also put some baking soda or drops of EO if you're worried about it though, I'm sure.