You are
definitely going to have to remove the drivers side tire to get to the plug easier if you are going to do it that way.
I installed my block heater back in 2006/2007. I travel to Northern Michigan a lot (up there right now!) and its not unusual for the temperature to be -20f in the winter time. The block heater helps a ton with getting the Envoy started and warming it up quicker. I love it and use it every winter.
IIRC, I used a few 1/2 extensions and a breaker bar through the fenderwell. I did it while the engine was warm,
not hot, to aid in removing the plug. Im pretty sure it had thread locker on it from the factory and it took some effort to break the plug loose