I'd make one change, if it were me. The way I did it a few years back when we ran our dryer vent out under the house {and used the same PVC for ducting} was I added a cleanout at both of my 90 degree turns. As you can tell from your picture, at some point in time, the airflow will be restricted to the point where you have to clean it out. having the PVC cleanouts in place just makes it a much easier job.