Very likely calcium deficiency.
I've seen it regularly among container grown veggies. Add some cal-mag to your feeding and I'll bet it improves, or stops worsening.
I love tomatoes... and having a home for them year-round is an added bonus of growing the Shrek indoors!

Oh and I WANT PICS!! Especially when they bear fruit.

What are you using for a pollenator? Do you have bugs, or are you going to do it manually?