My last truck had a 5/8 inch by 13 inch space between the frame and bed where I wanted the ball ( 6 inches ahead of the center of the rear axel) so I got a piece of steel to fill that space and extend outside the frame 1 inch on each side then I got a 2" X 5" channel Iron with 3/4" thickness and welded it under the plate. Used a magnetic drill to go first thru the bed ( 2 3/4" hole saw then smaller bit ( 1 1/4" ) to go thru the hitch. Welded the nut to the hitchafter the ball was in place. I used a 2 5/16 high shouldered ball with a 30,000# rateing that I ground flat sides on the shoulder. Over 200,000 miles pulling a WW trailer that is 37' long ( 7X30 box) and a tag trailer with buldozers, backhoes, trenchers. bobcats, etc. and have never had to work on it. I'm going to cut it off the old truck ( 480,000 miles on a 1 ton 4X4 chevy is all it needs) and put it on my son's dodge.
Even with todays prices should be less than $100.00 plus labor ( on rainy days my labor is cheap)