Do you just have a patio, or do you have a yard-type area?
If you have a yard, would a pond be a possibility? It would be pretty easy to make a relatively large one for probably quite a bit less then what a tank would cost (but would involve a bit of labor, so...), and the combination of sitting in the ground and being a large volume of water would provide a lot of temperature stability.
If not, I'm not entirely sure you would actually need to protect the tank from much, I doubt a bit of rain would hurt it (hey, free water change...), but if it's subjected to direct sunlight for too much of the day, it might get a bit warm, but it wouldn't be difficult to limit the sunlight (and, hey, free light...)
As to the power - just get an outdoor-rated extension cord, and run it up to a post near your tank, plug in your equipment, and stick an upside-down 5-gal bucket over that. It'll keep the rain out, but it will probably get full of spiders.
Throwing some pvc conduit or something won't hurt, and will also make it easy to bury the cords and keep them out of the way/keep people from tripping on them, etc. You might need to protect the individual pieces of electric equipment, etc., depending on what you are using. If it's outside, you won't need lights, probably not a heater either, but will still need filtration - if you just do something with a submersible pump, you are probably fine. for a cannister, you could probably do a similar thing with just throwing a bucket or plastic container over it (so long as it's elevated off the ground). Not real sure how to handle HOB filters...