I have reached that point in the building process when I install the cross-bracing in the aft fuselage. The manual suggests black elastic cord, but I am concerned about it stretching out, picking up fuel residue, etc. My thoughts are running toward using black monofilament fishing line. Anybody out there in RC Universeland have any experience/thoughts/suggestions on this delicate subject?

I use braided nylon fishing line. It seems to conform better at corners and bends than monofilament. I'm not sure what colors you can get... I have a beige sort of color in nylon and, for when I'm using the stuff as part of the actual structure, I have kevlar in dark green that usually looks black on an airplane. The kevlar is great, but way more money than the nylon.