opposite side of the muffler, under the horizontal stabilizer, as far back as you can get it. Try balancing your plane with a little piece of the weight sitting on the stab just above where you would install it to get an idea of how much weight you need. as said above, the further back the weight is, the more effective it is and the less you need. on my plane I cut a square out of the covering JUST bigger than the piece of weight to expose wood, then epoxied the weight on, coating the weight in epoxy.