I wanted to be able to do a simple smoke but retain the ability to use charcoal at times. At first I tried a single 1100W hotplate inside my 18.5" WSM, mechanically it worked and was cheap ($15) and easy, but the highest temperature I could get was 205F. That meant finishing everything my oven. Workable but not what I wanted.
So I switched to propane since my grill is next to my smoker. My first try used a King Kooker burner and a Gas One regulator hose. I could not get a reliable temperature below 275F. The burner was too large and the regulator hose could not maintain a low enough flow. I needed a smaller burner.
Try number three was the ticket. I used a Redcamp portable backpacking stove with a propane adaptor ($30) and a Gas One Propane Adapter hose ($7). It works perfectly, holding the temp at 225, but allowing up to 260 with just a slight adjustment. I put the stove on an old grill rack in the bottom oof the smoker, ran the line out the corner of the door, and put my chips in a foil pack in the basin (which I keep dry for this; filling it with water cools the smoker to much for the small burner).
So for less than $40 my WSM is propane whenever I want.