Robert,
I've check these out and while I have not made one I have made a few other things.Tthey do appear to be a simple thing to make. The only tricky bit would be shaping the aluminium tube on the mouth of the trumpet.
A vacuum pump would help but you could do it without one.
Just need to make a colapsable mandrel from plastic storm water or sewer pipe.
Coat it in PVA to act as a mould release and do you layup in glass and or carbon / kevlar. My understanding it the F18s only use glass but the Tornado ones are carbon & kevlar.

The ones I've seen slip the pole thru a couple of cylindrical fittings on the side of the trumpet.
These would be made seperately and glassed onto the trumpet later.

Regards,
Phill

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!