Zega Mundo/Pro/Pro2 Panniers - Owner's Experience Regarding Watertightness?

Can the Zega Mundos be regarded as watertight? Would the contents of a non-drybag be at risk (in persistent heavy rain, for example), necessitating the use of a drybag to keep undies dry?

TT's blurb suggests they should be, but IIRC, a YouTube group test revealed some small leakage. What are real-world owner's experiences?

I've got PRO2's, ridden a fair distance in pissing rain and there was a _very_ small seepage into one. Not enough for me to bother with drybags.