if this is for a unibody vehicle..?
the front bottom of wheel arch and end of rocker panel is indeed a very imprtant beam. I allow personally (and local inspectors that know better) NO rust there.. no patch jobs with miracle artist goop (bondo) .. it needs STEEL and WELD.
To reveal an extreme, my own car, I have got a subaru with diff lock that needed, not only a doubling of original, in areas you mentioned, but extra steel welded internally.. way beyond oem. Front wheel drive stay elusive, squishy, wiggling and comfortable.. but there WILL be a day when aggressive driving gets a blunt shove into your path and these problems are catastrophic.
NO rust in the wheel arches and rockers. I am not being extreme in mentioning it...
there is alot more replacement panels for cars like the escort, etc.. go for them, if it means keeping ugly seams for awhile, you can still be assured it is safe.
I have zero mercy on the rust in those areas. My locale nearly killed me playing these cheap games in the past.