The easiest fix, but not the cheapest, is to take it to a welding shop and let them rebuild that step area, my guess is that the metal is rusted out from being subjected to salted roads and not properly flushed out after such exposure. I would do a through examination of the whole underside to see what else is eaten away and ready to give you problems, pay particular attention to the generator supports, being on the back end that area will really get eaten up by salt.
Berniece & Russell with LilBit a Netherland Dwarf rabbit
1987 Southwind, 1995 Ford F150 Supercab 4X4 toad
Life in the fast lane? No thanks! We will stop and smell the flowers at every chance.