Trailors are almost always supported by cinderblocks on a wood board (not the best way). It sounds like the addition is sinking. Do you get a lot of water under your trailor?
You are better off having an expert check and adjust (maybe replace) the support blocks under your addition. I would not attempt to repair it myself. (Hint: Wizard of OZ)
I think any repairs to the floor inside the trailor would be temporary.