Need rv ladder advice...

I use an aerobic exercise step platform butted up against the bottom RV step (which is very shallow as yours is). It is exactly the same height and width as the bottom step and turns it into one big platform. And then I throw a door mat over the whole thing. It is much lighter than cinder block and can be stored up in the step well when traveling. You can find them in different heights or stack them as your RV requires. A while back I made a wood step that broke down for traveling but the whole thing was too heavy as you mentioned so I threw it away and went back to the aerobic step.