Short answer -- Yes, it will be miserable.
The pacific coast has a clear winter precipitation peak - whether oregon or Calif.
In Oregon, coastal areas can get 10+ inches of rain per month.
Even in central Calif you can have steady rain all day.
Plus the wind direction in winter is southwest - i.e. headwinds.
Plus temps in the 40s and 50s. Your tent will NEVER dry out.
Once, I hit a rare late-season storm in May.
I was cold, wet, and slammed by headwinds.
There are far better choices.
Your dates are te perfect time to do the Southern Tier.
The days are relatively short, but 8 weeks is usually plenty of time.
North of the ST, most camping will be closed.
(Then there's New Zealand)