We've driven our 40' motorhome towing on 101 all the way down Oregon to San Francisco. (daughter lives on north side of city). 101 will be just fine with your motorhome and you'll fit the tunnels.
From 101 at Santa Rosa - north of the bay - it will be 115 miles to Half Moon Bay.
Continue on 101 and at San Rafael get on I-580 taking you across the bay and thru Oakland
Exit 34 to I-238 west
Exit 16A to I-880 south
Exit 27 to 92 to San Mateo Bridge to Half Moon Bay Drive
Hope you can get your GPS to go the way you want to go. They're stubborn sometimes!
Perhaps your son would have different ideas.