For starting seeds, the biggest challenge (if you don't have a greenhouse) will be to keep them moist until they germinate. A very low frost cloth tunnel might work. A little micro-irrigation setup with timer set to mist the seedlings every few hours during the day would also speed things along.
Also, some herbs that came from the Mediterranean area really like dry air and hot sun. I do agree that in summer, something to protect the rows from the blazing heat would help a lot, but also growing types of herbs that are suited to more arid climates will be a good idea. Sages, rosemary, oregano, thyme, and lavender (which they already grow commercially up in the deserts of Mona, Utah) would be good.
If you want to grow herbs that need more moisture, (like Basil which does great here in FL) then something like a frost cloth tunnel might give a 20% or more reduction in sun intensity, and also hold in a little bit of humidity. It would also help extend your season, as you could start plants earlier in spring and hold them longer in fall.
