MAC Performance Rocketry sells some very nice "Ready-to-Fly" nosecones that are specifically built to hold the TelemetryPro transmitter. They are available in 3" and 4" sizes in either fiberglass or plastic. They use a PVC threaded closure with a Kevlar lanyard. This eliminates any metal parts from being near the transmitter downlink antenna yet is very secure.
The fiberglass nosecone is filament wound and has a canvas phenolic coupler that is exceptionally strong. The tip on the fiberglass nosecone is aluminum.
These are high quality nosecones that eliminate the need to build your own. They are Multitronix approved!