I dragged and dropped them on the RW icon
Have you made sure that you used the right icon (latest version)? Have you restarted RW after installation of your new stacks?
The best way of installing add-ons (in my opinion) is to drag them to RW icon in the dock, because this way you know you are installing them into correct location (unless you have left an old version of RW in the dock).
but I can’t find them within the RW program
I don’t know where exactly have you tried to find them, but the way to do that is to click on Addon button in the top RW window bar. That will open a separate window. Select Stacks and then Control-click on a stack you want to find in Finder and choose Reveal Addon in Finder.