Welcome Baja Bob,
I think the recommendation to drive 40 West to California is a good suggestion … although I'm not as familiar with this route as others maybe. But I can suggest the rest of this trip North with experience. … After Barstow, Ca head up to I-5 North and continue to a small farming town called Williams ( north of Sacramento) and here you have a decision point. Listen to weather forecasts for the Siskiyou Pass right on the California / Oregon border. It is here that you are most likely to find a snowy and icy road. If not too bad keep on heading north on I-5 …. if heavy snow is forecast then I'd suggest you drive west on Highway 20 to Highway 101 and follow that north to Aberdeen, Washington. Next choice then is to head for Olympia and I-5 north or continue north on 101 to Port Angeles / Port Townsend. At Port Townsend you can ferry across Puget Sound and I-5 North to Bellingham. Ferry will want a reservation called ahead.
On your return trip with trailer, many people stop for first night at the KOA in Lynden … to sort things out (pretty close to Chillwack and Sumas border crossing). Near by Bellingham has a Walmart (free over night in their parking lot) and a Costco. Gas at Costco is the cheapest around and samples are free, the $1.50 hotdogs and $5.00 roast chickens are a deal.
Back to driving south …. no question I'd ferry over to Port Townsend, camp there - Fort Worden. Next day or when ready follow 101 on around the top of the Olympic Peninsula and south. 101 is much slower than I-5 but oh so much more beautiful. This time of the year, daylight hours are pretty short and 101 has lots of camping opportunities.
Enjoy your trip … I wish I was going too!
Tom