I have a floor in my 7 year old trailer that is soft in the busiest part of the trailer. You feel the support floorboard, but it is soft on both sides of it. The floor in that spot creaks like an old ...
What Make and model is the trailer? Where is the soft spot? Does the floor have carpet or vinyl on it. If vinyl you can tap the floor with the handle end of a screw driver and see if you here a difference in the sound of the soft area versus what doesn't feel soft. If bad will have a soft thud sound verses a sharp tap sound. If sound is different then worth further investigation.