Best Water Resistant Roller balls?

Hey All,

Lately I've discovered pilot V5 and v7's and very much appreciate the needle tip rollerball more than most gel pens. I ordered the v7's from Japan which take pilot cartridges to refill with fountain pen ink in an attempt to have a permanent black rollerball. It's not bad, but of course not as nice an experience as their proprietary cartridges or the liquid ink in their non-refillable versions.

Anyway, someone on here posted about their uniball roller haul from office Depot and mentioned, I think, that they're highly water resistant, which got me thinking: which good rollerballs are a) water resistant or (gasp!) permanent and b) refillable (either with official refills, cartridges, or otherwise).

I'm aware that they make rollerballs to be used with FP ink-- it interests me, but is not what I'm looking for here with this post.

Thanks for any tips, folks! Happy writing. PEACE