If you're growing in a pot and it's really hot outside, and you've had problems with BER on your tomatoes, then water is probably the issue. Lack of it, that is. If you can put something to rig up a little shade on the outside of the pots, like set something in front of them between them and the sun, or pile mulch all around them or a bale of straw or something, to make the roots not get so hot, that would probably help too.
I've just never seen potted tomatoes that do as well as ones in the ground, and they're a lot more work to keep up. Are you fertilizing them regularly too?

Thank you for responding! Since they are in Miracle Gro potting mix and compost, I was only fertilizing lightly once a month. I will try increasing that. Our temperatures are down to around 90 for the next week or so, but if they go back up around 100, I will move them around so they get more shade. I do see some scorching on the leaves. I will also step up the watering to every day, I was doing it about every other day. My neighbor is giving me some grass clippings to mulch them with too. My ground soil is hard red clay with NO drainage, and would take a lot of work to make it growable, which my back and I can't do. Sounds like I am still making some classic newbie mistakes, lol. Thanks for your help.