Cheap but Reliable Thermostat?

[Chkadii]

This is slightly off topic, but... How do you set up a backup thermostat?
I have a herpstat 2 on my rack, and the heat tape is wired to a lamp cord, which plugs directly into the T-stat. Where does the second T-stat come in?

At risk of derailing the thread (though it looks like OP made their decision), here's a diagram I created at work because I'm a huge dork: