Even when the temperature was moderate outside, our motorhome’s large shower/tub skylight used to let in too much heat, 
causing the air conditioner to kick on when it wasn’t really necessary. Plus, there was simply too much sunlight coming in through the skylight into the bathroom. My solution was to paint the skylight on the exterior with white liquid rubber roof coating. Using blue painter’s tape I first masked off a small band at the base of the raised skylight. I then applied two coats of Conklin’s Rapid Roof III Top Coat. It’s a fairly thick product and is fast drying, so I applied the second coat almost immediately
after the first. As soon as I was done with the second coat, I stripped off the masking tape for a clean, crisp edge. The skylight is now about 70-percent translucent, allowing some light to pass through while truly blocking most of the heat from the sun. The coating has been on for four years now and has shown no signs of fading or deterioration.
Thomas Mosher, Spokane, Washington