call hardwood flooring finishing guys if you want a super smooth floor. Ask around for one who uses a planer, opposed to a sander. You can get it smooth as glass, then urethane on top.
Epoxy would work great on wood! Garage tiles as well (Swisstrax / Racedeck)
I'm not sure if I totally understand the construction methods, so some of the above might be a problem if the wood is moving a lot.
I'd love to see a picture of the floor, but also whats below? is there insulation?, Is the wood resting on the ground?
S.