A plastic tote/storage bin works well for a nest box. You'll want the substrate, I used a sand and peatmoss mix, as deep as 2/3 the length of your biggest female. The substrate needs to be moist enough to dig a hole that holds shape. The turtles will track substrate back into your tank. They will also do their best to fling it over the sides of the box. You need to make sure the ramp to the nest box and the box are escape proof so they don't take a tumble. In the long run I found it easier to set up a temporary enclosure with a kiddie pool and tote to move the female to. Either way its a fair amount of work, but worth it. Hatching baby turtkes is way cool.