I can tell you what I did at a previous residence which I think you may be able to adapt to your situation if you are handy with a hacksaw and file.
Lowe's sells a die cast weatherproof cover for a two-socket receptacle with cords plugged in. The brand name is Tay-Mor or Tay-Mac as I recall. It's big enough to hold a standard X10 Appliance or Lamp module in the upper socket, but of course there's not enough room for a plug into the module.
The advantage to this particular brand of cover is that the catch is off to the side, so you can hacksaw and file a slot in the center of the bottom to clear a plug without screwing up the catch. (I actually used a Dremel tool with a cutoff wheel.) A 3-prong plug will protrude a little through the slot but the contacts are protected from rain.
Now Lowe's also sells a matching die cast surface mount box which will hold the receptacle, so the plan is this: You wire a plug cord to the receptacle though the bottom hole of the surface mount box (use a cable clamp), which will be plugged into your existing outside outlet. Attach the modified cover, and hang the whole thing on the wall near the existing outside outlet.
If you need more modules at a particular location than there are sockets in your existing outside outlet, get a wire-on plug and connect two or more cables to it - the cables which you will wire into the surface mount boxes. For safety, use 2-wire + Ground cables.
(I don't know if there's a 2 gang box and cover, but it wouldn't be wide enough to have two modules plugged in side by side.)
Note: The "Codekeeper" brand of cover sold by Home Depot has its catch at the center, so won't work.