Its not the turbine are you need to worry about, its the area around the pipe. If you dont have good airflow around the outside of the pipe you can get some pretty high radiant heat temps. The warmest outside fuselage temp I ever got was on a BVM t33 at the end of the pipe. It was pretty tight there and it got to about 142 F. I would probably get some thermal insulation and line the foam around the pipe and turbine exhaust cone. Keep as much clearance between the pipe and foam as possible. Remember that much less heat transfer takes place >1/8th inch from the source. Scotty