Well, to be perfectly honest, Patrick, the amount of corrosion that could occur under that little of tape might be minimal as it probably would under a small seizing - although there's room for variance with how much tape one applies and how tightly it's taped. I think that I'd be a bit more concerned having a split metal washer sawing around the wire with every spin of the roller. If I had to install a roller I would probably go with small seizings of either stainless seizing wire or some sort of small stuff like tarred seine twine and then make a little split washer out of a bit of plastic to act as a bearing. I'm sure that the professional riggers on this forum probably have other opinions. Whatever you use to hold up the roller, it's still going to require maintenance (which was a consideration for me). Tape sticks for a while but most stuff degrades pretty rapidly with UV exposure.
You might find that the slippery tape works for you on some areas but I haven't tried it on spreader ends. I have found that any tape on spreader ends tends to get quickly worn away by the genoa and that the tape, in turn, tends to not be as gentle on the sail threads as I'd like it to be. Maybe I just don't use enough tact in my tacking.
