BEST WAY I EVER LEARNED... was drivers Ed. It was awesome. they'd put a 1"x1" stick in an orange cone. That was a "car". we did parking, straight and parallel, and the goal was to touch the stick but not knock the cone over. This was cool. by the time you hit the stick, it's already tipping away from you and has the cone off-balance. so the cone is very ready to fall. You HAD to touch the stick. And you could NOT tip the cone over. I learned the boundaries of the vehicle better that way than any other. I plan to take my daughter out and do this drill with her, then my son.
My truck is the hardest vehicle I've ever had to back up. You wouldn't think it-- trucks being so square are usually some of the simplist. But for some reason mine has never been natural. my back window is a little smaller and the tailgate is pretty tall. I generally see the top 1/2 of the windshield of the car I'm backing up to.
So I have to plan ahead. I check where the other vehicle is relative to the white line before I start to pull in. Then I back up to where I know the line to be. I know the line is 3' behind the center of my back wheels. yep, sometimes my head comes out the window to sight it. I also use reflections in the cars next to me, or shadows between bumpers to show me the size of the gap. At work, I know that the dividing lines to my L+R are the same length as I am--- so if I line up on the front of the line, the bumper is at the back line.
I can and do parallel park it, even downtown. But I'm not as precise as quickly as I can be in a small car. I may think I'm about to touch, but I've got 18". It's hard to remember where the bumper is when I can't see the the hood.
My wife and kids generally don't drive it--- it's hard to park.
It gets worse in camping season. did I leave the ball in? How much longer is that? (I generally don't have it in unless towing, BUT let's say it's a grocery run right before pulling out.... there's another 9" of pokey steel back there).
Still, the only reason I thought of putting a camera in is to sight the tow ball. I've thought about it -- neat tech, could be kinda handy.... but I decided I'd rather take my time, go slow, and line up the markers. I feel if I'm gonna drive it, I need to be competent enough to drive it.