In storage, how were the jacks/stabilizers used and could the surface it was on shifted (over time or due to weather, i.e. freeze/thaw heaving)? What I'm getting at is that if there is any difference left-to-right between the weight on the stabilizers or jacks, that will put a twist in the frame that the floor will translate up into the walls as a shear force.
Not sure if you have a TT or 5er but when I park my 5er, I am always very careful to use a combination of 2-by lumber and plastic levelers to get within about a 1/16" difference under the landing gear side-to-side before starting to lift weight.
Not trying to place any blame - stuff happens - just trying to find out to keep others from having the same problem. Sorry about your luck.
2015 Rockwood Signature UltraLite 8282WS Platinum, GY Marathon LRD, TST 507RV TPMS
2005 GMC 2500HD CCSB D/A, Curt E16, Prodigy P2, Garmin RV760LMT w/BC-20 b/u cam