I prefer the weld/bolt option, though OOP'S set-up is a nice simple way w/o having to do anything to the frame.

This is how I have made the slider mounts in the past for a few rigs.
I weld the mount to the frame, and then bolt the sliders to the mount. For X-cabs I like to mount the sliders in 4 places, and use a ldder type design. This takes a little more time but any impact to the slider will be spread over the entire slider and frame, rather than to a limited area. I also prefer using square tube, it is nice to stand on and provides a good lifting point for a hi-lift jack.

I have had to remove my sliders a few times as well. to paint and replace the body mounts. Painting could have been done with them on the truck, but not the body mounts, if they had been weld on I would have had to cut them off.