As for L-shape you mounted it upside down. IMHO. Short piece should go flush underneath frame rail and welded on the other side kinda like those cross-member/body mount/trailing arm attachments. This way any lifting loads on rails would try to twist entire cross section of frame instead of trying to deform (expand) long face. Those holes are for plug welds as well.
Here is what I mean:

or like this depending on size

Like John says, the gussets go a long way for support. Check here http://www.ballisticfabrication.com/Cage-gusset-with-holes_p_1185.html
You can find them cheaper if you do a search on line, just be aware of the sizes. Both the size of the gusset and how much space you have underneath the slider and amount of frame to weld to

Ok checking Trail Gear website that's pretty much what they show


Looks like holes might be used for bolts as well. Look like a good thought out product.

You all need to stop picking on my dear son, you hear! <img src="/forums/images/graemlins/smile.gif" alt="" />

Maybe breaking off a slider is better than bending a frame. Just saying.

You know, in a way I'm just glad I don't have sliders - but then I've been thinking that I really do want some.....

-BUT-

If I get some, I probably won't post any pictures..... because the Slider Welding Police might come for me..... and that would be bad......... really bad.... at least for somebody. <img src="/forums/images/graemlins/evil.gif" alt="" />

With only my college engineering class experience from 45 years ago (and unused since), I stick-welded an exhaust pipe stack for a 16,000 lb deisel loader today.... for the 4th time in 6 months.... because vibration keeps breaking the pipe. Try welding the thin stuff with a stick welder for fun. <img src="/forums/images/graemlins/scared.gif" alt="" /> I'm sure a really good welder could have done a better job, but you know what? Every time I reweld it, I learn something new and by golly, today, I think I got it right. Maybe someday I'll be a good enough welder so I can tell others how crappy their welding looks. <img src="/forums/images/graemlins/lol.gif" alt="" />

Frank <img src="/forums/images/graemlins/cheers.gif" alt="" />

Even when you get to that point, Frank, you'll still be polite about it. Maybe that's a Southern thing, I don't know. I do know my Dad taught me to say nothing if I couldn't be nice or offer something positive. I didn't say I've always followed it....

LOL, don't you worry Michael & Frank. I got this. I hope I've shown through the years that I welcome "constructive" criticism. What I won't tolerate is someone bashing others just because they don't know any other way to get their point across or any other stupid reason. <img src="/forums/images/graemlins/rolleyes.gif" alt="" />

Just go test 'em and see if they hold. If they don't redo it. If they do, it's good welding.

I like really pretty welds on an aluminum tuna tower on an expensive sport fishing boat or on engine bay stuff..... but for what you're doing - form follows function. <img src="/forums/images/graemlins/kewl.gif" alt="" />

<img src="/forums/images/graemlins/cyclops.gif" alt="" />On the underside of an offroad truck, pretty is as pretty does.

Frank <img src="/forums/images/graemlins/cheers.gif" alt="" />

The weld looks strong to me. Although I don't think it looks good, mine would end up worse than that, but whatever. If you look close you can see the plate melted into the weld, the weld to the frame should be just as good.
<img src="/forums/images/graemlins/kewl.gif" alt="" />

yah did mount it upside down though <img src="/forums/images/graemlins/wink.gif" alt="" />

Post deleted by blueeyeddevil