Thanks for the suggestions. EVTripPlanner shows I should be able to get from Surrey Supercharger to Glacier, WA, do two day trips to Mt Baker Ski Area and return to the supercharger on roughly one full charge of my 2013 Model S 85 (it shows ~75kWh required). Using Blaine Supercharger as start and end point, it shows ~62 kWh usage, but there are no L2 chargers between there and Glacier for top ups.
If I can get a top up by Brodeur's Bistro on the way there and back and plug into 110V while parked overnight I should be OK.
This reminds me of a trip from Vancouver to Calgary/Drumheller that I did in 2014, before there were superchargers along the route. I haven't really had to plan out charging stops in advance like this since that trip.