Also, an option might be to use those elbows used on handrail assemblies call "Keyclamps" I believe. They use tubing and have elbows that utilize setscrews.
I found this website so everyone knows what I am referring to:
http://www.svl.ie/index.php?pid=107&cid=83
My only concern with u-bolts is if they start to slip and slide. Maybe a set collar below the lowest u-bolt to prevent downward travel?