I borrowed and tried using a Hovabator for my surprise clutch of ball python eggs, and the tub wouldn't fit inside.
I was watching Snakebytes, and BHB just uses shoebox tubs with HatchRite in the room. But then again his entire room is 85*. For just one corn clutch, maybe that would work for you at this time. That would give you more time to get set up with something more elaborate for the other snakes/turtles you plan on. (For me and corns, that room idea would work best for US, as all of our snakes (but 3) are in one small, temp-controlled bedroom, set at 84-85*.
But I too, am looking to build an (igloo) cooler version of incubator for the balls.
I have an old refridgerator, and once working again, will convert IT to an incubator. It was free, and I've been lugging it around the last 3x I've moved

, just so I'd have it to convert.