I have thought about this a bit, I have looked at the designs available for bolt on sliders, and well....... I think they lack a some in reliability when compared to weld on sliders.
Here is what I think, I hope it isn't inflamatory, just an opinion based on personal experience.
Self tapping screws in an aplication where there is bound to be quite a bit of flexing and movement such as sliders, is not a good thing, eventually they are going to come loose or fall out. Ya just can't torque down a self tapper like you can a grade 5 1/2 inch bolt.
It seems several designs on the market with bolt on sliders take this route, for ease of installation and I believe ease in fabrication, but I don't think it makes for as strong of a bracket attachment as welding.
I am not 100% sure what the best answer is for a bolt on slider that is easy to install, easy to fabricate, and doesn't crush the frame, or use self tappers that will fall out next year, if not by the end of this year if the slider is used repeatedly each month.
While welding has its own down sides ie you can't just hack weld them on there as some one else suggested, and if you want them off for repair or sale you have to grind them off which can be a pita even with a small grinder. But they are are solidly on the frame, which means they flex with the frame, there isn't anything to "torque" down so nothing can come loose unless the frame or slider catastrophically fails.
The thought that I am mulling over for my sliders is a combination of the two types of brackets. Making a weld on bracket with bolts welded onto the face of the bracket. The bracket would be made out of 3/8s or 1/2 inch, it would go across the full width of the frame for 8-10 inches in 3-4 spots along the frame. I would use large 1/2 inch or greater mild steel bolts to make it easy to weld them into the bracket. Then the slider could be bolted to the bracket that was welded on the frame, therefor easy removal of the slider, but a bolt on design that could be torqued down decent enough to not work loose, not crush the frame, and still reliable.
Anyways some thoughts or ideas on the subject.