“You said to put the heat source inside but dont you have to put water inside?”
No. You regulate any moisture requirements in the secondary containers – the boxes or deli cups with the eggs and moistened substrate – which are placed inside the incubator.
“Also my heat source would be a human heat pad. I thought you put water inside, some bricks and heat source underneath outside.”
Again, you’re thinking of a different design. But regardless, the function of the insulated box is to keep the heat INSIDE. Applying the heat outside would be counterproductive.
Taking everything into account, if I wanted to incubated small numbers of gecko eggs needing low 70’s temperatures, I’d buy a Hovabator or something similar. Far more cost effective – cheaper than one good proportional thermostat. The nice thing about building your own is that you can design something to do double or triple duty over the course of a year. Make it big enough to serve as a nursery or quarantine facility as well as an egg hatcher. Obviously, I’m talking about something bigger than a styro box here, however.
-Joan