IF housing your outside long term is your idea, I suggest building an outdoor enclosure completely. Cattle feed troughs are great especially if you want to keep more than one dragon....it can be sectioned off or just have a group of females in it. The top can be covered with heavy screen to keep bugs and predators out.
Round or oval shaped 'pond' tubs could be used outside too...just make sure it has some way to drain, so a heavy rain won't flood it.
The important features you want in an outdoor cage are areas dragons can get out of the sun and cool down (either by burrowing, hides, shaded tops etc.) They should be protected from predators or kids from getting at them (predators can be the cats, hawks and eagles flying over head, seagulls, crows, ravens etc.) Rains should not threaten to flood the enclosure, either by having a sloped roof or lean to over the tub, or a drainage system so ran flows out of the tub but still can keep the dragon inside, even if he manages to dig to the bottom. (not completely sure on the methods that can be used)
Several southern located breeders use outdoor setups completely, and their websites may have hints... doing search on the forums for outdoor cages or enclosures and checking the cage/enclosure forums, can help as well. Most outdoor cages can easily be adapted to suit dragons even if the design is for some other reptile.
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PHLdyPayne