We've used Hypervent on our cutter for several years and it has worked beautifully at eliminating moisture/condensation under the mattress. We just bought our trailer a couple of weeks ago so don't have a lot of time with it, but based on our previous experience on the boat we decided to put it in the trailer too. I'm thinking it's probably not as much of an issue with the TT as with the boat where the berth was below the waterline but I figure it can't hurt (and I had enough on hand to do the short queen in our FunFinder).
Daz