I suggest SUNRISE YACHT PRODUCTS, in Fl...
Multihull Nets and Trampolines for Catamarans and Trimarans, main page
They make great multihull
nets & tramps, that are strong, and REALLY last. You can get the mesh, in light or heavy, Phyfertex, heavy webbing, or net.
They made ours 16 years ago, out of the med weight mesh, and by taking care of them, and re-coating with their vinyl dip twice, they're in GREAT shape, STILL!
You will not save much by making them yourself. (This, coming from folks who built most of their own canvass, & boat)...