There are some new PLA-derivatives (like Makergeeks' Crystal Raptor HTPLA) which, after a little bit of annealing treatment, look pretty good for long-term outdoor use. With an after-treatment glass temperature of over 200°F, they appear to be up to the task of outdoor weathering.

Which reminds me, I need to make that particular experiment and see what happens when we are a little closer to summer. I have the stuff, I might as well give it a good going over!

The other thing to be careful of with 3D printing and actual structural supports is keeping in mind how much infill versus how thick the external shell is. A solid piece of extruded plastic is going to be expensive to print and take forever, but it's going to be ridiculously rugged in every direction except across the layers. Even PLA, as long as it doesn't get hot. As you decrease the amount of total plastic in the piece, strength goes down.

But you would be amazed at how little plastic you can get away with and still have a piece that serves its structural purpose.

Again, as long as you're not applying force across the layers.