Are they covered? After two seasons of pure endrot I bought a shabby little "greenhouse" to grow my tomatoes in. Fingers crossed for this year.

Aw, that sucks. Last year a big rain caused this in a third of my roma tomatoes, I was so sad.
I'm now the proud owner and user of a calcium spray to try and prevent this.

Amish trick. Spray your tomatoes with milk. The calcium stops blossom end rot. Spraying milk is also effective against many tomato fungus.