Camp site width?

Pulled farther forward than you think you should. When backing, as you've noticed, the turn starts slow then goes quick. Once you figure that out, with practice, it will become easier. I can back my 42' FW into tighter spots than my 8' cargo trailer.

Find a large parking lot and set up five gallon buckets 12' apart and practice backing. I have small orange cones I lay down for the path I want to follow when I'm by myself and backing into a tight spot

Good luck

I feel your pain. I also could put my travel trailer wherever I wanted and have issues with the fiver. The biggest challenge is getting your cut line right. If you feel like it is wrong, pull forward and start over. Fifth wheels react slowly and there is seldom much room to correct in a campground. It is a good feeling when you know you have made it on the pad. Small corrections are simple when the truck and trailer are pretty much lined up. If you can back in 90 degrees to a 12 ft. road, you are in good shape.

Measure the width of the trailer, add 2 feet. Don't strive to be good enough, but be the best!

12 feet ought to do it.

We have been in numerous sites where the pavement or gravel drive is not much more than 2-3’ on each side of the wheels. Get some cheap orange soccer practice cones at Walmart, go to an open parking lot ( I used a school parking lot on a weekend), and practice.

From my experience, there is no average. Sizes are all over the place. Put some cones out that are a couple feet wider than your trailer on both sides.

What I was told when i first started with horse trailers was

when going forward, to wait until it seemed almost too late, and then turn hard.
Backing up, turn a little bit seemingly almost too early, and then watch for the trailer to react, and then follow it.

School parking lots on Sundays, maybe a large manufacturing facility, and use the lines to learn your rigs characteristics.

Campsites generally are less than 20 feet wide and that is using some of your sitting area.
Think about the ones you frequent, likely they only have about 4 feet extra on the drivers side and no more than 10 or so on the passenger side.

Once you get used to it. It is not a problem. I found that backing up the 29ft. Fifth wheel is a lot easier then my 7ft utility trailer.