Thanks for all the tips! I tried out an A frame setup last night (but cheating, between two poles) and it worked well, though I need some extra rope to secure the tarp at six points instead of just four. I think I might go with an A frame type setup in the desert, since I'll be with other people who are using tents and I can probably tie my ridgeline to their tent poles! (Unless that's a bad idea for some reason - is it?)
And I can also let one end down to the ground to have only one end open, facing away from the wind. Of course, the wind last night seemed to alternate coming from two opposite directions, and is generally kind of wild and unpredictable here, but what can you do?
I'll probably take my hammock into the desert for the bugnet, using the tarp ridgeline to hold up the bugnet loops, just in case of any weird things that might be crawling around the sand and rocks. Then once I hit trees I'll make everyone else in the group jealous for the rest of the hike.
Anyway, I'll report in a couple months on how it went...
One more thing, I'm looking for cheap, light things to use as ground cloths. It's surprisingly difficult to find any variety of outdoor gear beyond the basics here (already in Israel) and especially DIY stuff, but I was thinking of just taking a few black plastic trash bags to thrown under my tarp. They an also be used as an emergency pack cover or poncho or something. Any problems foreseen with this? Other than durability - sure they're kind of likely to rip on the ground, but also not hard to replace. And they are next to free and weigh nothing.