Z248F seat base replacement

I'm in the process of replacing the plywood seat base for my mower and after getting the cover off the bottom I was floored that the plywood base is not sealed sufficiently to keep water and moisture from rotting the wood.  It was a hot mess after 3 years of owning it and it very, very rarely was wet.  You'd think they would have soaked these seat bottoms in something to seal them better.  I'm figuring the total cost to repair it at around 25 bucks vs. the absolutely insane price of a replacement OEM seat.  Even 'cheap' seats aren't cheap.