It might be a pollination problem with the hubbards, rather than BER. They look like they're forming squashes, grow to a certain size, then start browning from the blossom end if they haven't been pollinated properly.

Bt works on cabbage worms. You have to renew it everytime it rains, but other than that it's a viable, organic solution.

A friend of mine, who raises butterflies, says sprinkling flour on the plants deters the cabbage butterflies from laying eggs. In her words, they see the flour, think that plant already has been colonized, and go on to a different plants.

Does it work? Beats me. But is certainly a cheap enough experiment.