Thanks, All, for your comments.
Regarding weather issues, I had a number of problems with the previous enclosure: To save money, I used 1/2" EMT conduit for all the support poles, and the corner poles and a couple of others at the ends of the structure got bent during our monsoon winds. I straightened them out again and sleeved heavier conduit over them, and haven't had any more bending. However, the new netting has smaller openings and therefore will likely create more wind resistance, so time will tell whether the poles will be able to handle the load.
On the first version I used cheap tie wire for the rigging that supports the netting. In a fairly short time, though, the wind began to make the wire fatigue and break at the connections, and then the netting would tear. The wire also rusted, which made it abrasive and caused it to wear through the netting in some places. In the improved version I used 1/16" galvanized aircraft cable instead, sleeved inside 1/8" irrigation tubing. The tops of the support poles are kept from touching the netting by shields made from 2-liter soda bottles, cut in half. The tubing and half-bottles insure that the netting only comes in contact with smooth plastic (except in a few spots along the edges) which should make it last longer.
We rarely get snow in Tucson but it does happen, and during one winter storm there was enough buildup to tear the netting. I can't engineer it to carry a snow load, so in the latest version I'm planning to remove the netting after harvesting the last persimmons (around Christmas), and reinstall it again in April before the first apricots ripen. The vertical netting at both ends of the cage is permanently installed, but the rest is a simple rectangle held in place with clothespins and wire hooks for relatively easy (I hope) removal.
The other main climate issue is sunshine. UV eats most plastic up pretty fast in Tucson. The previous netting was pretty stable, and still in relatively good shape after four years. The new stuff doesn't seem that durable to me, but we'll see. I used Dacron multi-stranded fishing line to connect the seams; it should last much longer than the netting itself.
Unfortunately, it's inevitable that this sort of light-weight enclosure will require periodic maintenance and repair. I've worked out some of the bugs but I'm sure others will appear. I just hope there won't be any problems so serious that I have to give it up, because in my area, a physical barrier is the ONLY way to keep birds from spoiling most of every crop.