I replaced ALL of my fender flare attachment hardware with Nutserts, though not stainless steel. I did use Never Seize on the screws - I can take my flares on and off in mere minutes...
It seems that a lot of you "bag on" Nutserts - I've been using them since the '90's - prolly installed a thousand of them on ~20 different vehicles. I've attached door panels to fiberglass doors on 5 vintage Corvettes and on every one of the four Jeep Wranglers I've owned - probably had "issues" with less than a dozen of them. Worst case, remove the bad nutsert and install a larger one - I LOVE 'em! I used 'em to hold my side steps on too; here's a pic of the fender flare Nutserts:
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