Yeah funny thing, mine is rusting out at the front, driver side body mount, right by the power steering box. The back of my frame (where it usually rots) is pretty solid. For some reason the driver side floor is rusting out alot faster than the passenger side floor (in my 89).
My 99 has no rust problems, i only wish the 89' was like that.

89 4Runner
3" BL, M/T locks, 33"bfg mt, bilstein, Kayline, tubebumper, toyotafiberglass panels
TBI: Elocker,3.4 w/ORS,b+b,S2Sstg2cams,arias pistons,P+P intake,TRDs/c,URDpullies+7th,downey headers,MAPECU2,WEGO WB, SupraMAF,walboro255,stg4clutch, EPaOo2 sim