I've only been 5th wheeling for 5 seasons. I still embarrassed myself. :) Sometimes it's the mirrors, other times I miss the mark 2-3 times. Sometimes I nail it on the 1st try. If the site is on my left when backing in and visibility's good I can usually nail it. On the curb side it's harder.
A backup camera is on the spring to do list.
Part of my problem is the DW. She still doesn't understand that the 5er reacts slower than our TT did. By the time I get the "Go that way" message, I'm too far into the procedure. If the sight is gravel I drag a line with my foot and say this is where I want the 5er tires to go. The other thing I found is to go SLOW when backing up. If you go too fast you'll overshoot your correction point.
I'd much rather back up a TT any day.