Cottonwood
Roadster#433, Model S#S37
I would not recommend using any extension cord less than 10 AWG, regardless of length, and keep the length at 50-feet or less. The Model S can detect resistance in the cord and will not allow a charge if the voltage drop is significant.
Incidentally, did you look into Destination Chargers (HPWCs) in Maine? A number of hotels and resorts have them. Some may require that you stay there, but others might allow you to charge while stopping for an extended lunch.
It's total resistance of the circuit to the car that will trigger the 75% charge current (12A->9A) safety feature. With a good starting 120 outlet (circuit) I have successfully charged with 50' #12 and #14 extension cords. Those #10 cords are pretty heavy and will only save you from 9 Amp charging on a few threshold circuits.
I recommend a good #12 50' cord with quality plug and receptacle. Here is one example: US Wire 74050 12/3 50-Foot SJTW Yellow Heavy Duty Lighted Plug Extension Cord - - Amazon.com