Thinking about how I would compose if I were a trumpet player,
I came up with these ideas:
1) Improvise and record voice #1 on the trumpet.
2) Listen to what you have recorded and revise until you are satisfied
   with it.
3) While reproducing voice #1 on a high quality audio system, improvise
   voice #2 on the trumpet and record voice #1 and #2 on the same track.
4) Repeat steps 2) and 3) until you have the desired polyphony.
5) Enter the notes generated by 4) into a software program which will: 
   a) permit you to simulate various classical instruments assigned
   to all of the several voices you have composed, and
   b) permit you to print out scores for various instruments.
6) Record your composition as played by your orchestra.
7) Publish a CD of your recording on Amazon.com CreateSpace at no cost.