I've been asked this question a few times over the past few months so I thought I'd turn my reply into a blog post.
Hey Eric, I'm looking to buy some soft good or vinyl wraps for 12" box trussing. I wanted to check with you to see if you have a company you would go with for something like this. Let me know if you do, I'd like to order them as soon as possible. If you don't know of anything, no big deal, I'll go with a company I found online.
I'm honestly a fan of Visqueen. Cut into 3' wide strips, wrap around 3 sides that the audience can see - adhering with Gaff tape. A light from inside will glow the Visqueen and highlight the truss for a really great looking texture.
Another thought to consider is pulling fabric through the inside of truss. Again, position your truss warmer inside the truss as well - the fabric will take color and play with the folds for beautiful saturation while the truss will be highlighted in silhouette to for additional texture and form.
Below are photos showing both ideas in use.