I feel your pain...
When I had a similar situation, I didn't use any kind of weatherproof cover; rather, I got a large can, and mounted several receptacles in it, using standard boxes and covers. I also cut, and bushed, some 2" holes in the bottom edge for cord access.
In short, I made a very large "in use cover." The best part of this approach was that there was plenty of room, for even the largest plugs- and enough receptacles for every cord!
