I just installed a block heater on my 2016 and this post was very instructive, thanks!
The only thing I would add is that I found it helpful to remove the rubber lining inside the front driver's wheel well so that I could reach through there to seat the cartridge. (I didn't need to remove the wheel, I just reached around from underneath the truck.)
Also, to anyone scoffing at the idea of a block heater in the lower 48: I'm not so much worried that my truck literally won't start. It just makes me feel better to have the engine warmed up as quickly as possible. Where I live there are maybe 10-20 days per winter when it's still below 0 ºF in the morning and I always wince a little hearing the engine struggle to turn over. Plus let's be honest, anything that helps get the cabin up to temperature faster is nice.
$50 + 1 hour well spent, I would say.