Hi Clawdia,
Oops … I didn’t have the chance to go back through your posts last night and I only remembered that you had a waterbed foundation.
The bed rug would lower the risk with any solid surface although with the conditions you are describing the risk of a solid surface would be lower than if your sleeping environment was higher humidity or warmer. There is more about this in post #10 here.
You probably wouldn’t have an issue either way and FWIW … I use a solid surface (our adjustable bed) because the benefits of the bed were worth the higher risk of a solid surface for us. It really depends on how much “caution” you are most comfortable with.
Phoenix