I've recently mounted a few extra tie downs in the bed. I plan to mount more in the near future. I drilled out one side of the bracket to fit the larger shank on the factory bolt and used self tapping bolts for the other side.
Redrider I just loaded tapatalk app and am viewing the forum from there for the first time and I see that it doesn't show the captions with the pictures. I explained what each picture was. I showed the package because this particular brand from lowes lined up perfectly with the tailgate latch bolt holes. Without going out to look I think there was only about 5 tie downs from the factory and only 1 was actually in the bed floor. It appears they only put them there for the net and some accessories in my opinion. I'll probably add several more.
I did drill 1 extra whole per mount in the bed. I reused the factory bolts in the center and added a self tapping bolt for the other. If you tap on the picture to enlarge it you can see what I mean. The ones on the tailgate I did not have to drill, they are the factory bolts.
Here's a closer look. The black bolt is factory and the silver galvanized one is the self tapper. I used a pretty good sized self tapping screw so it should hold well.