I had the same problem in my unit. It was about 5ft to the left of the entry door. Turned out to be a broken weld on one of the cross braces that go between the frame rails.
Had to open the bottom up and remove some insulation to get to the area of the squeak to find exactly what the problem was. Fixed the broken weld and everything been fine since.
Hope yours is a more simple fix.
sam
Sam Nivrig
2001 F350, CC, 4WD, PSD, DW
2009 Select Suites 36RESB3
2002 Alpenlite Limited, Cheyenne 950