Here is a tip you can use to make a support-insert for the boom on a round fuselage tail boom. On my 500 size MD500D, I didn't have one in the box.
I picked up this material from work. Its used in tool box draws where they cut out a trace of the tool. This is stiffer foam.
I cut a piece a little bigger than the boom hole
Then I tape up the tail to avoid chipping around the edge
Using hand pressure, push the foam onto the tail, and twist back and forth, to
let the fuselage do the cutting...apply just a little even pressure at a time
The perfect cut!
To make the hole for the boom pipe to stick out of your new insert, just use the same method by using the helicopters boom as the cutter!
A spare hobby king HK500 blade holder is about the same thickness (1/2in) as the material I used, and will work even for a 450 size. Keep in mind that this will work only on a ROUND fuselage tail boom!