I did build a shelter for my Traeger, when I first got it. This picture is from 2011:
I've since added a GMG Davy Crockett to the collection, which won't fit alongside the Traeger, so it is where those chairs are, so in the open. However, the power sockets I am using are still covered (they are proper external sockets with RSD, but I am happier that they are under cover as well).
I've had the GMG since December, and it doesn't seem to have suffered at all. I have a cover for it, but to be honest, I don't always bother to put it away properly.