Thanks!
You could do two smaller Meph in a regular Earthbox. If they are larger girls, I'd only do one. If you have the light, you can grow some real monsters in an Earthbox and you can easily fill one half of a 4x4.
That's good info. The seeds are Skywalker and Forum Stomper under a HLG 600rspec. It's plenty of light when I can get the heat output under control!
Saw the comment above about moisture levels and made a note to watch for it early on. My plan was to plant directly in the EBs to avoid transplant stress but it's an important detail that I hadn't initially considered. Much appreciated!