Just to throw in a wrench: from RBI, the tanks stack three high and so do not take up more room than an RBI rack- okay, fine, maybe a wee bit longerbut really no big deal. Females get larger than males (typically) so when they are nearing breeding age, the tub size you'll need will equal the space of three cages stacked. Also, one Helix controls all three cages. Also, heat/humidity regulation is no prob in these cages- I even use paper substrate and have no problems holding humidity. Just sayin.....!!!