If boom comes loose, it can move
around while the plane is flying causing all kinds of problems. It can also
twist so that the tail is no longer aligned. This links shows you how one
person
secured the boom on their plane using screws. One concern with this technique
is that the threads of the screw could abraid the control lines or the
receiver antenna. This might not be the best approach
http://rclibrary.com/viewtopic.php?p=34#34
If you look at where the boom is attached inside there is a pinced area. I
drilled a small hole through the top of that area and through the boom. Then
I put a 4" nylon tie thorugh to help secure the boom. I also put packing tape
around the boom and the back of the body where the boom exits. Between the
two, the boom is well secured.