This is a topic of much discussion on this forum. I think someone did a poll once, and it turns out that slightly more people use tanks than tubs. Tubs do have lots of advantages but I still prefer tanks. I feel your pain with the space issue. I'm moving my BP up from a 10 to a 20 gallon tank soon. She is growing so fast. I have the 20 gallon tank all set up with (almost) the right temps and humidity. I'm sure I'll get it soon, and then I'll make the swap.

I was concerened with the fresh air issues too, until one day when I overmisted the tank (I don't need to mist anymore) and could actually "see" the airflow in my tank due to the condensation on the walls. With openings at the cool end to let fresh air in, and openings at the warm end to let it out, the air flows in the cool end (and because cooler air is heavier than warm air) it settles to the bottom and flows across the bottom to the warm side where it is warmed and rises to the openings in the warm end. I don't know how anyone could maintain temps and humidity without covering most of the top (just like a tub).

There are lots of helpful links to setting up a tank on this forum. I have discovered a great way to cover the top. I cut a piece of 1/4" plexiglass to fit perfectly into the 1/4" recess in the top of the tank. Then I drilled 1/4" holes along both ends (cool and warm). The 1/4" recess in the top of the tank allows the plexiglass to sit flush with the tank top so you can just pop on your screen cover as usual. I also tape foam board on the top of the screen cover, taking care not to cover the holes, and three sides. Works like a charm.