Are you taking your RV or travelling by car?
By avoiding the section of I-5 from Redding to Canyonville, you have missed the bad passes on the freeway.
But freezing fog, or high winds, can be issues on the coast road, at that time of year, and I've never driven OR 20.
I've driven the I-5 in mid, Dec and had very bad roads, thank goodness I was just in my toad, family health issues meant I had to return south Jan first and bring the coach back Jan 10, so three times over the route in just over three weeks, both Jan. trips weather was not an issue.
If you have good weather either route will be fine , but there could be a very short period of good weather that time of year.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.