If the heater you're speaking of looks like this, you should be able to use it.
This type of heater has a fan in the back, and heating coils in the front.
In order to make this work for heating an incubator, you could wire a thermostat of your choice directly to the power cord, and that thermostat would shut on/off this heater to maintain heat. The problem you would face, is that even when the heating element isn't on, you need a fan to circulate the air. So in order to make up for the fan being off when the thermostat shut the whole heater off, you would have to get another fan. About 8" or so. I recommend getting a metal fan from maybe the dollar store, or wal-mart.
Although the method above would work fine, you could simply get inside this heater, and wire the thermostat directly to the heating element, and instead of the thermostat shutting the whole unit off, you could have a working fan, and the heating element would shut on/off like it needs to. And this wouldn't require you getting another fan either.
Without the thermostat shutting the whole unit off/on, the fan can stay on continuously.
If you do decide to use this heater for your incubator, MAKE SURE IT IS SECURED DOWN, AND CANNOT MOVE. If you use this, make sure that you remove the cover on the front. It is directly in front of the fan, and the heating element, and not only does it block air flow, it also causes a safety hazard, because these heaters weren't designed to be used for 21 days OR MORE at a time. I don't think there is anything wrong with this heater, I believe it will work great. I would make sure that the fan is on full blast when you use it though.
Also, if you do go into this incubator build 'head first,' I would like to help you in any way possible. If you need help, just message me. I will reply sooner or later.
By the way. I don't recommend using the water heater thermostat with this heating element. Actually I don't recommend using a water heater thermostat in a fridge, or cabinet incubator. They work very well in small incubators. I have a cooler incubator uses one, but I don't recommend using them in a fridge or cabinet incubator.
I would recommend using a wafer thermostat, or a Bi-metal thermostat.
I have used both of them, and I like both. The only thing I don't like, is that the wafer thermostat requires a new wafer about every 2 years, and the bi-metal thermostat can be used about forever. I have an old friend that has an antique roll-x incubator, from the 70's, and it has the original bi-metal thermostat in it to this day. And this incubator works great.
I would recommend the bi-metal thermostat, but the wafers have NEVER let me down. Wafer thermostats can be used for most all temperatures, but bi-metal thermostats can be only used in temperatures of 80-105. The wafer thermostats can be used to control various temperatures, but the bi-metal thermostat can only be used in a 80-105 degree environment.