Just parked at FastPark for a spring break trip, most of the L2 spots were taken by various EVs, but there were at least 2 spots open. I opted to park on the side at the L1 spots (120V 20A GFCI outlets) instead. There were a few spots ICE'd, and 3 other Teslas were charging, including a Model 3! I chose the L1 partially because I wanted to leave the charge at 50% for most of the trip, then ramp up to 90% about 40 hrs before. You cannot usually do that at the L2's, as you will usually get unplugged. I think that is reasonable if it shows you are not charging. Each L1 spot has their own outlet.
The L1 outlet I was plugged in did pop the GFCI at some point, but I called the customer service number and gave them my spot number, and they hit the reset button for me. This happened last time too, while the car was not actively charging, storms maybe?
I highly recommend using these spots for longer trips, the more we use them the more awareness there will be against ICEing. There was a white Model S parked in one of the L1 spots without being plugged in when we got back, maybe they forgot their UMC.