I sprayed mine for a week with PB. I went to take the first one off, snapped before I even put any real pressure on it. The second one I tried to baby and it snapped, 3rd I tried to tighten slightly before loosing, snapped. The last one I just gave in and let it snap.
I then beat on one of the stuck nutserts for a few hours with a mini sledge and it didn't budge. I ended up cutting the floor to get to them(was easy) and found the stuck nut was Welded not tacked. Each nut had a thick slag of weld covering 1/4 of the nut, then the 6-8 tack welds under them. I see no way that beating it from the bottom would have worked.
All 4 bolts were rusty, I have zero rust anywhere on my jeep but those bolts some how got rusted.