I promised I would report back after I did this.
For a little background, I just bought a 4 horse trailer with a 4 short wall dressing room. I do have plans for finishing this out in a weekender type camper this winter, but camping season is RIGHT NOW. I need to be able to use this for sleeping and storage, as is.
I bought the ceramic insulating beads from Hy-Tech and added them to my own paint. I tried to match the trailer, but missed a bit. I bought 1 gallon of latex satin exterior paint, and 1 quart of the hy-tech paint thinner--needed after you add the beads. I painted the interior of my dressing room with one coat of this paint. I did some touchups where it seemed thin. I will say that this ended up being a very textured paint.
I camped in this last weekend. It rained off and on so we had PLENTY of humidity. On Saturday morning, I woke up and put my hand on the ceiling above me. It did feel slightly damp, but there was no visible condensation, and certainly nothing raining down on me. I have about a quart left, and plan a second coat in the gooseneck above where I sleep. I am not sure I would do this for a permanent solution, but it sure works as a temporary one. And over the winter, I can add the foamboard and paneling right over the paint.
If anyone has more specific questions I would be happy to answer them.
Here is the website for Hy-Tech. http://www.hytechsales.com/insulating_paint_additives.html