The second support tube never hurts; Especially if the sliders themselves use 0.120" thick walled tube, which is light for a rig over 4k lbs.
If getting it custom made, get thicker walled tube, say 0.134" or more, it will hold up better if you actually do anything that tests them.
The basic styles are the old school flat bars that stick straight out from the frame...they are easy to make, nothing changes if you get a BL, other than the rocker panels they are supposed to protect being even FURTHER away, etc. They don't have bump-outs to catch on rocks and trees, or other protuberances to get caught up on.
Their ground clearance is the worst of the styles, as they come straight out from the frame rails, and they protect the worst because they don't come up to protect the rockers. (Worst doesn't mean they don't work, it just means all the other styles are more protective, etc)
The second style mounts to the frame rails, but comes out, and then up, to protect the rocker panels. Its harder to make, but improves the ground clearance, and is more protective of the rocker panels. These are also smooth and devoid of protuberances to get caught up on things. If you get a BL, they still fit, still make a good step, but, are less protective as the rockers are now a few inches higher, etc.
A BL version curves up HIGHER, to compensate for the rockers being a few inches higher, and to provide MORE ground clearance, etc.
A BL version of this style will NOT work W/O a BL, as w/o the BL, the rockers will be too LOW, and the lower door edges might hit, etc.
The showier versions of either style add protuberances that can get caught on things and hurt clearance, but which make better/wider steps.
The further out a slider sticks, the longer the lever arm that is created, and the more force an impact has on the mounts, longer tubes, etc. Try to snap a full sized pencil, vs snapping a little stub....its easy to snap a long pencil, and all but impossible to snap the stub, the lever arms are too short to get enough force, etc.
Same for a slider....the shorter the tubes' run, the stronger. The further it sticks out, the weaker it will be/the more gusseting/bracing it needs to compensate.
For the same wall thickness, a round tube is stronger than a box tube. The wider the box cross section, the weaker it is across the shorter span (The better the step the worse the protection). Imagine a plank of wood, like a 2x4....lay it flat over a ditch, and put your weight on it...it will sag in the middle, or even snap if there's a lot of weight.
Turn the same 2x4 on edge, so the skinny side is up, it will now support a sheet ton more weight. Same concept.
Round tube can be 1/3 thinner walled, and still be stronger than the same wall thickness of a boxed tube...or the same wall thickness, but a lot stronger, etc.
If getting sliders made, thing about all of this.
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