Been there, done that.
Not on a WR-250R, but on my XT-200J dual-purpose bike in the olden days.
You can count on some corrosion if you ride the bike during the winter, especially if you do it a lot.
Typical areas of corrosion:
Drive chain.
Rear wheel spokes.
Rear shock linkage.
Swingarm pivot.
Frame front down tube.
Front of engine crankcase.
Front of cylinder head and cylinder.
Mounting bolts and studs for exhaust head pipe.
Exhaust head pipe.
Exhaust muffler.
Horn.
And, eventually, electrical connections if it's done long enough.
As said, washing the bike well after each ride and finishing the job with a lubricating spray at the trouble spots will help a lot, but I'd be surprised if you don't finish the winter without some traces of corrosion.
If it's your only wheels, I wouldn't be paranoid, but I would expect to do a lot of bike washing and lubricating.