Some more info might get some replies.

I had Sausage tomatoes this year. Out of all 6 varieties the the Sausage was the only ones with BER.
Three varieties in the same row, 5 varieties in the same bed & the two Sausage tomatoes had BER.
I think it is the Sausage variety, not the soil, heat or water.
I am going to try them next year with bone meal, if I do not get 1/2 good fruit, then they are gone for good.

When you speak of rotting could you please share with us where the rot is on the fruits for there are several pathogens that can cause what's called spots and rots on the fruits.

Is it at the blossom end and you see a leathery lesion which sometimes turns black when the area is invaded by normal fungi from the air?

Or is is splits in the fruits along the sides or elsewhere that start oozing white stuff?

Or do you see fruits that look like bags of water that are swollen?

Anything you can share with us about this rotting of the fruits can help/

What also can help is if you tell us if you're growing inground or in containers and if inground how far apart are the plants b'c in your zone 8 if plants are too close there's lack of air circulation which really can cause fungal infections of the fruits and also the foliage.

Carolyn