As you know the important thing when going forwards is wider turns. Take them to a lot and take something it won't hurt to run over to show them this. Cones or even rags put down on the ground for "curbs". This way they can learn that turning with a trailer is not the same as without without damaging anything.
Next, teach them how to stop. Disconnect the trailer and have them get up to whatever speed you have room for and brake hard from a designated point. Now mark where they stop.
Hook up the trailer and with the brake controller turned all the way down, do it again. This will show them how a trailer adds to stopping distance.
Next time adjust the brake controller and do the run again. This will give them confidence that the brakes on the trailer can do their job as long as you adjust them properly and give space to use them.