Damp under mattress

[DennisB]

Hi, we recently found dampness underneath the mattress of our 2020 trailmanor.
There is no obvious leak. We have been in pretty cold weather and using our heater quite a bit. I wish to avoid the nightmare of mildew so I am asking:
1. Anybody here experienced this?

2. If so, how can it be prevented?

Thanks,
Dennis