Hi ebrowndo2;
Welcome to the forum.
A temperature controller such as the Auber PID (mentioned by Toker), would be your best solution. If that is not within your budget, there are less expensive brands out there.
Another alternative is to purchase a wireless thermometer that monitors the temperature and sends the results to either a remote monitor or your smart phone. Not only will you be monitoring the cabinet temperature but your food temperature. The placement of your third party probe also matters. If you have it too close to the food you will get a lower reading than the actual cabinet temperature. Keep that probe at least a few inches from the food.
With the digital smoker you are going to have swings; as much as 20°F. Unless you are smoking sausage, lox, or even bacon, these swings shouldn't be too much of a concern, and by trying to adjust the temperature during these fluctuations is not necessary.