How to Overlay??

Hey all,

I've been wanting to create a portal to the moon, or another planet, or... somewhere in space; while in space, I want there to be an air bar on the bottom of the screen, similar to the health bar or the food bar, but most similar to the air bar when underwater. Basically, you'd have little O2 marks at the bottom and they would disappear over time. Once they all disappeared, you would die. There would also be blocks you could stand on to replenish your air and an air tank you could use to keep your air up. I've tried using the overlay mod element type, but it's either uncomprehensive or not the kind of overlay that I'm thinking. Is there a way to add this via MCreator, or should I post something in the ideas forum section to add this later?

Thanks,

  -A