I don't mean basic relative to all porteurs, but basic relative to your design. So on that one you showed, if the perimeter wasn't stiff enough, a few short struts between the two perimeter levels would create a truss, much stiffer. If the tubes that make the platform weren't stiff enough a few pieces connecting them would make them share the load better. If the verticals were wobbly a strut tying them together would keep them more in column. But the trick is to come up with a design that allows these kind of changes to flow. So that you don't a have stage one looks great, stage 2 looks like stage one with a lot of hasty additions. It's not a big mystery, just plan ahead. Or get a design you like of some complexity, and strip it back, then if it isn't strong enough, you could go for the full build.
A lot of porteurs just have a flat rack, that would be basic, a second level tied in as a truss would be stage 2, etc...