I haul a full-size quad in mine and can't use the factory tiedowns, can't reach them when the quad is in the truck tires are in the way.
I took four 5/8-11 bolts 1 1/2" long drilled and tapped them to 3/8-16 drilled four holes in the bed set the 5/8" bolts in with fender washers on both sides now I can screw in 3/8" eyebolts when I want to tie something down or remove the eyebolts when I don't and put the a plastic panel push pin in each to seal the 3/8 hole when not being used.
They work great and put the load into the floor instead of the bed rails.
I have seen someone selling them or similar style somewhere I am sure you could Google removable eyebolt or something and find them.
edit.... found this almost the same as what I did http://www.bedbolts.com/