So I looked up what information I could find about Whisper Canyon. It looks like they might have more than just "regular outlets". They have RV hookups. That usual means either 120V/30A TT-30 outlets, or even 240V/50A NEMA 14-50 outlets. At the very, very least, the "regular outlet" would most probably be a 20A NEMA 5-20.
If I were you, I would:
a) bring my UMC with 14-50 adapter and 5-15 adapter.
b) buy a Tesla 5-20 adapter
c) buy a TT-30 adapter (eg.
NEMA 14-50R to TT-30P Adapter for EV Charging at Campgrounds)
d) Optionally buy a 50A extension cord (
https://www.amazon.com/Camco-55195-Extension-PowerGrip-Handle/dp/B0024ECIP0)
Let's say you only have 20 hours of charging. Using your regular 15A Tesla adapter, you would get about 60 miles or range in 20 hours.
Using the Tesla 5-20 adapter, you would get about 85 miles of range.
Using the TT-30 adapter, you would get about 128 miles of range.
Using the 14-50, you would fill up completely and then some.