If you want some really labor-intensive wet weather streamers, start with some paper towel stock. The rolls of white, institutional paper towels with no perforations. Dye it orange or purple, and then, after it's dried, strip it using a paper guillotine.

We actually used these for 1/2-A Combat at the 2001 Nats. For the big stuff, we used plastic tablecloth (not biodegradable, though).