Extension Cord Cover?

Hi all, maybe someone can help me. At some point in the past I was looking at RV accessories and saw something that I thought looked like a good idea. It was some kind of plastic box that snapped over the connection of your trailers' electrical cord and any extension cord it may plug into. It would protect the junction from getting wet in case of rain and help hold the connection together. Well, now that I looking to buy that item, I can't find one. I find them that will cover 2 regular  extension cord plug and socket joints but that is not big enough for the trailer plug. Does anyone know where I might find one of these? (Camping World does not show one.)  Does anyone use one of these? Does anyone know the proper name for one of these?
As always, THANKS for your help.