If it were mine I would seriously consider filing a report with the NHTSA Office of Defects Investigation (ODI). I've seen at least one other complaint for frame rust on 2008 and newer T4Rs. If enough reports are filed, it might just get the National Traffic Highway Safety Administration to take notice and get Toyota to 1) fix the bad frames, and 2) make the new ones better.
File ODI Report and Check Other's Complaints
Date Complaint Filed: 11/18/2012
Component(s): POWER TRAIN , SERVICE BRAKES , STRUCTURE , SUSPENSION , WHEELS
Date of Incident: 10/01/2012
NHTSA ID Number: 10485047
\Crash:No
Fire:No
Number of Injuries:0
Number of Deaths:0
Manufacturer: TOYOTA MOTOR CORPORATION
Vehicle Identification No. (VIN): JTEZU14R180...
SUMMARY:
THERE IS CORROSION IN THE FRAME AND DRIVE-TRAIN COMPONENTS. THERE IS PITTING, RUSTING THROUGHOUT THE FRAME UNDERCARRIAGE AND THE SUSPENSION AND DIFFERENTIAL COMPONENTS. THIS BARELY 4YR OLD VEHICLE IS A SOUTHERN VEHICLE. REGARDLESS, THIS CORROSION IS A SAFETY ISSUE IN ANY VEHICLE LET ALONE IN A 4RUNNER WITH A SERVICE INCEPTION DATE OF 11/30/2008 WITH 19K MILES. THIS IS TOTALLY IRRESPONSIBLE OF THE MANUFACTURER AND THEY CLAIM IT IS NOT COVERED BY WARRANTY. YES, IT (SHOULD BE) COVERED BY WARRANTY AND MORE IMPORTANTLY IT IS MANUFACTURER'S LIABILITY TO CORRECT SAFETY/QUALITY ISSUE. *TR