I'm sry Dan, I did not catch that you had planned the plastic floor coating.
1st of all, marine grade plywood would have been advisable for the subflooring in an environment such as yours.
Then, I would have suggested a heavy bodied oil based stain for the floor of a workshop. Some of the exterior fence stain products, blended with others perhaps for a color base. Penofin was a good one, back when.
Only a matter of time before mold grows in between the substrate cellulose and the plastic skin of an acrylic stain, or urethane. Sometimes they even begin to scale off...
An oil based stain can be swabbed on, then touched up at any time.
Question. Do you have plenty of under-floor venting? ...that won't be blocked by snowfall ?
Best
rc