So some late night working going on (and only one nail in the foot and a few cuts to show for it)...got the rest of the rubber and rotted plywood flooring up. Turn out the rust was worse in the middle than in the back (and not so coincidentally below the shower and toilet's former location). On the other hand today we had scrubbed the floor with a wire brush on a stick and one on the drill and then coated it with purple power rust stop. It worked great, especially after two coats.
A little dark but the view from the front (disrupted by our saved wood bridge)
So much for avoiding a northern bus to skip out on rust, she's a salty sea bitch for sure.