A while back FMCA had a tech tip about a plastic rain box for the electrical cord. Specifically, the plug the 50 amp to 30 amp adapter. A 
number of folks have reported electrical problems when this connection gets wet during rain storms.
The plastic box keeps the rain out of the connector.
It is easy to make and does the job.
Addendum If I were doing this today, I would consider the "throw away" plastic containers from Glad or Ziplock. They are cheap, easy to use, and easy to replace.
Doug
doug@rexhalltips.com