There are a few different options here. First, if you or someone you know is handy and has a few tools, a thermometer can be mounted in the smoker cover fairly easily. Here are instructions for mounting a grill thermometer.
Of course, you can also use your kitchen thermometer in the top vent. If you plan to leave it there constantly during cooking, be sure that the dial or face is heat proof.
What I love to use is my Maverick ET-73 smoker thermometer. It has two separate probes, one that goes into the meat, and the second that attaches to the rack, displaying the smoke chamber temperature. These are great!
