I feel you frustration and it seems as if you have all of the typical bases covered: Lack pollination is the major offender usually, but you have that down. When you water, are you watering deeply? Irregular watering can cause blossom end rot, although this seems to be less likely in squash than tomatoes... It is common for the plant to abort the first few fruits until it gets to a size to support the fruit, but it seems like yours are problematic beyond those first few. I don't know what to tell you, except that you sound like you're doing all the right things. The fact that you're getting the female squash blossoms in abundance says to me that the soil and sun factors should be ok. Hopefully one of the more experienced folks like Farmerdilla or Weird Trev will have some insights.

If it makes you feel any better to share some of the pain, I planted Cavilli F1 Hybrid zuch's this year. They are supposed to be parthenocarpic - no pollenation required. So I gleefully grew it under netting thinking I would defeat the SVB this year! Alas, I watched no less than 10 zuch's abort before I finally took the hint and started hand pollinating. So I know how frustrating watching that fruit abort. And the one and only melon that formed on my vines, split the other day and I had to cut it off and throw it out. Sigh.

Best of Luck on your squash problem. Hope someone else has something more to offer than sympathy.
Susan