Thanks again. That second sill is one of my considerations although I do not believe from the last time I was under there that it was too close. However it warrants a look. I will remove it temporarily and see what happens.
Another spot is where the regular bed bolts go thru the steel strips and at one point on either side it is again very close to the frame kick-up over the rear axle. So close that I cannot put a washer and nut on the bolt as there is no room.
First thing tomorrow I am going to remove that 'floating' sill and let you know.
I am carrying a big spare tire and a tool box in the bed. The tool box is bolted down however - I reversed the bolts that go through the bed strips and put holes in the bottom of the tool box with the bolts coming up thru. The spare is just sitting there and I have removed it to check for the clunk but the tire is not guilty!
