My main sheets run paralel and outside the boom, and my boom is 23 feet long.
I have a few "eyes" shaped rectangular and then I hold the shhets from coming down with velcro straps.
Here is a photo of the metal pieces I talked about
And here the set up I believe I would do in your case. I had that in aboat I owned in 1990.
And if you need to run them outside look at this set up, it shows the eye and the velcro strap. I but these at WestMarine for a few bucks.