I would never trust any plane to be balanced out of the box.....especially the "RTF's"

On a trainer, I wouldn't worry about lateral balance at all. Later on, when you get into some aerobatics, you can worry about it. At that point, you would first try and move the battery and other moveable electronics to the lighter side of the fuse. If that doesn't work, then you have to work out further on the wing, and cut into a bay. Go to the last bay so that you will have to add the least amount of weight.
Always epoxy your weight. i wouldn't trust the self-adhesive at all. Especially on Fore/Aft balance. If you just stick them on the tail, and they fall off in flight, now what? You have a tail heavy plane to try and land in one piece. I would go one step further and cut the covering and epoxy the weight directly to the wood. If you can get inside of the fuse, even better because then it would be hidden.

However, as suggested, always try balancing with what you have first... i.e. move the battery back, go with a lighter prop, lighter spinner, lighter nose wheel, etc. Try to not add any additional weight. remember, light is good when it comes to flying.