the wiley window doesn't hold the water in the lip at the bottom, that lip has drain holes at the front and back that drain the water back out to the outside.
The windows were designed for sailboats, one guy who had them on his boat sailed around the world with them, he never had a leak even from rouge waves or wakes. In the harbor you take the glass out completely and store it somewhere else, since your trailer won't be facing rouge waves or wakes (wait I take that back you do live in a flood prone area

) .... 99% of trailers won't face waves or wakes, unless you are ridding out a hurricane no precip should come in with the glass removed that the drain channel can't deal with.
I believe this picture would be more instructive,
http://www.google.com/imgres?imgurl=htt ... CFMQ9QEwBQ the name "wiley window", AFAIK was given to them by Phil Bolger a man who had a huge influence on the plywood epoxy DIY home built boat building world, he owned a boat designed by a man name Wiley. Since no one else has claimed the design the name has stuck.
I'm putting them on my TD door right now, I'm going to use plain old plexiglass for the glass with the option of changing the glass for a sheet of plywood when I want the light blocked/privacy. with an "eyebrow" over the window, a window screen bedded into the opeing, and a slightly larger drip tray, I don't think I'll really need the glass to keep out rain that often, probably only put it in for towing. I already have curtains for privacy anyway.