Also, you have to seal these lights very well.
They appear to be designed to leak. I can only guess that they are designed to fit on a flat vertical surface that also has the wire hole in the vehicle sealed.
There are two water vents in the backplate, one in the top and another in the bottom. Old RVs like ours have corrugated metal panels so the backplate cannot sit tight against the panel thus leaving large gaps. Also, the wires go through a 1 inch hole through the wall. So you need to caulk completely around the installed light and make sure to cover the vents.
I would only use LED lights as the lens/light itself is usually sealed. The old style lights also have holes in the front of the backplate for the wires and the lens doesn't seal well either. These ones leak like crazy.
