Kathy, if I may?
The tarp will surely prevent rot, but I do believe there is a trade-off in not getting those Orchids, which need to be in the sun to bloom, (like Schomburgkias, some Laelias etc) truly used to bright sun. Is it perhaps possible not to use a tarp, but use a fan ( yes, even outside) to dry up the plants quicker. It may not be practical for long periods of rain, but for those Summer showers it may not be so cumbersome?
Now I live South of you and do not use a tarp or a shade cloth ever over my sun-loving orchids. And yes, I do lose every Summer several plants due to rot, not a good thing. But some of the Cattleyas have still live eyes and start to produce later growth. So not all is always totally lost.
As I said - I would call it a trade-off? Tarp = no rot, but less sun = less blooms?
In your case I would consider rigging up something different to protect them from the sun only during the first two weeks or so outside, and then slowly skip the protection for the sun-needing Orchids. No netting after the initial "getting used to be outside".
Something to think about?