I sure wish I had the ability to attend more of your workshops. Do most RV manufacturers use butyl tape under the items they attach to the exterior of the RV? Is using multiple 1-inch strips under all of the area of the accessory necessary or can I just go around the edges of, say, a 4″ x 4″ item? —Robert W.
Yes, it is the norm for manufacturers to apply a layer of butyl tape (otherwise known as putty tape), or some form of sealant/weather-proofing, between components and the exterior surfaces of the RV during installation. In fact, to prevent leaks, it’s a mandate.
However, it’s only necessary to apply the sealant (personally, I use Eternabond DoubleStick tape) under all the screw locations or around the flanges. You don’t need to place additional strips unless it creates a mounting or balance problem for that device. I’ve never seen that happen, by the way. But just a layer under the flange perimeter of whatever the widget is, where the screws go through, should do the trick. Just be sure there are no voids or gaps between the accessory and the roof or sidewall. Notice how the window in the photo here needs new sealant!