Extendible cables are not available yet for Teslas wall plug-in 3rd generation (hardwired, stationary charger).
The NEMA 14-50 extension cord would be appropriate for use with Teslas mobile and Teslas plugged-in wall connectors, gen 2.
This charging cord will work with any Tesla vehicle that requires type-2 plugs at the infrastructure end,
which is the case in most European countries, with the exception of France.
All the destination chargers will have covers on the connectors,
And as long as you do not put your cable in contact with an element, this does not impact charging in the event of a rainstorm.
I noticed in Teslas manual about their mobile plugs, that it has a warning saying you should not put it outside in the snow, heavy rain,
using during electrical storms, or any extreme weather conditions.
In Teslas manual one of the warnings is to NOT use mobile connector when you, your car, or the connector is exposed to heavy rain, snow, electrical storms, or inclement weather.