Awright - if I understand correctly (short, left welded sections get holes, then bolted to underside of camper, tabs welded to bottom of short links such that tabs and short-bent section of long link butt, therefore putting pivot bolts into mostly shear load outward and downward) then I think a max of 250lbs may be OK on the step.
But, the first hole closest to the pivot in the left, short link will see (IMO) maximum bending strain, so the stop tabs you're speaking of would ideally go past that bolt hole on either side, i.e. two ~1/4" triangular plates, each about 3" - 4" on the weld leg and stop tab leg (hope this is clear).
With that setup, the weld legs of the stop tabs would reinforce the outside bolt hole, helping prevent it from bending.
What I'm not so sure of is lifetime - pivot bolt area should be ok with lubrication and not huge cycles, but the shells may oval with a lot of stepping. The bend zone on the long leg will have strain hardened a little bit, allowing more deflection without plastic deformation, but will still be subject to "unbend" if excessive loads are placed on it due to impact or whatever if the load weight's not uniformly spread between the two bars.
I'm also not clear about the wood step - is it going "up and down" along the picture axis (perpendicular to the two long links)? If it's as long as you say (32"), then there's obvious risk of stepping offset to the stainless bars, therefore putting a twist load into the assembly - this is much more complicated from a stress standpoint.
