I'm not a frequent visitor to these forums but I'll show you how I've made my rack:
It houses 5 adults and 4 babies/juveniles.
Keep in mind that I'm from the Netherlands, and we get our tubs from IKEA, not sure if you guys have the same ones to fit. (these are 79x58x18 centimeters)
heated by 7 UTH pads and hooked up to a Thermocontrol II thermostat.
This has cost me approx 300 euros total. I live in a one room flat (student type of apartment with 2 roomies) so it had to look quite sharp to fit my living :p
Greets,
Yaron