A Ranco certainly would have been better than the wafer thermostat that comes with the Hovabator, but I agree with Heather, I use a Helix for my incubator.
Incubators are so easy to make, and I've heard way too many horror stories about hovabators - there are some success stories, but there were too many tragic stories for me to ever trust a ball python clutch to a chicken incubator.
I use a mini-fridge that has a fan and a strip of flexwatt and a Helix, and I've (knock on wood) hatched 5 clutches in it so far with no issues. I know that's not a large sampling, but it's been worry free.
Deborah made an incubator using Degei's design.
http://www.eyehit.com/degei/supportf.../inc/index.htm