A good tub to use would be a sterilite 1790 tub, you can get those at any walmart or target. Its a 41 qt tub, if you can't find that, just find one with the most floorspace you can, any vertical height in the tub above 8" or so is just wasted space that they won't use.

Once you get that, you can get some flexwatt heat tape to run belly heat on the back floor of the tub, probably about 1/4 of the floor. Hook that up to a thermostat and you'll be good to go. I recommend using a proportional tstat like a helix or herpstat, but a ranco or jc would work also, just not as good, for half the price of the proportional stat. You wouldn't need to adjust your temps for night-time heat. Unless you are cycling your animals for breeding purposes, a night-drop is not necessary. Just run normal temps 24/7.

This style tub will be awesome to hide under your bed or somewhere like that once you get to college. They are actually meant to be storage boxes for say, under your bed.

I think that covers everything you asked above!