Your best bet would be to get a rack setup if you plan on expanding your collection and breeding. A rack is by far the best way to give your animals the conditions they need. These snakes live in holes underground in Africa. They like small dark spaces and would be much more comfortable in a rack setup than in display cages. You can certainly keep these snakes successfully in the type of setup you are interested in but it would not be ideal and your breeding success may be hindered. If you want to use that open rack with tubs just run some flexwatt heat tape along the back for belly heat. I think of my snakes as pets as well but I also realize that what is best for them is a rack setup. I do keep one snake in a display during the off season but the rest are in racks. An enclosed rack offers the best sense of security for the snakes and is easiest to control temperatures.
You will need a thermostat to run the flexwatt.
Get flexwatt at www.reptilebasics.com - they also sell good racks ...
Thermostat - www.spyderrobotics.com
Put holes in your tubs using a soldering iron... this will leave smooth holes that will not have sharp edged for your snakes to rub on.