Chris, a drop or two of pool algaecide will help to keep the pans from growing so much green gunk. You could also spray the louvers with diluted algaecide once in a while to keep them clean.
I recently bought some at Home Depot, and the smallest size is a quart. (I use it to keep the patio under my orchid growing area from growing green stuff). If you know somebody with a pool, or a pool cleaning business, you could maybe get a small amount from them to use for this.
