I suppose too many people submit posts on squeaky floors, but wanted to post what worked for me. After having horrific issues in 3 areas of our unit, found that the screws Jayco runs down through the under layment and through the steel cross bracing were the cause. After accessing from the underbody, took vise grips and tightened the screws, then put flat washers and 1/4 NC nuts on the bottom side of the screws and tightened. No more squeaks. Summation of the issue was since we use the hell out our TT, the screws pull through the steel cross bracing from travel, and make intolerable noise. All is good and won't have to trade it now as we were going to do! Hope this helps those who have this issue.
East Bound & Down- We Love Camping :)