Ummm, it is on wheels. Between those wheels & the frame there are springs. Springs are designed to, well, spring, whether the pressure comes from the road or above as in people walking.
The only way to convert a trailer into a house is to take the weight off the wheels by jacking & blocking under the frame. Not worth doing for stops of only a few days but worthwhile if you are a seasonal & the trailer does not move for weeks at a time.