Hi, bear in mind that Alicante and Gardeners Gelight are types of toms that do grow outside well anyway. I grow my plums in the greenhouse but I choose for high yeild. I grow La Roma not Roma, it has 7 times the yeild and better disease resistance, I have grown them outside but I do get earlier results in a greenhouse. Another point to remember is many Roma types have a longer growing season Re the blossom end rot, I tend not to worry about it much, I find it is the first toms of the vine that seem to be affected, later ones seem to be fine.
XX Jeannine