Number of plants in an Earthtainer

[ArthurDent004]

After seeing how big my indoor tomato plant has become, a neighbor has offered to let me put a container or two in his backyard. I was thinking of building a earthtainer out of 14 gallon Rubbermaid Roughneck containers. Would two determinate tomato plants like a Silvery Fir and an Early Wonder do well in the same container or should each plant have its own container? The Fir isn't supposed to be more than two feet tall and both list 55 days from seed to fruit. I thought the shorter growing time would be good if I'm trying to start this later in the year.

My other concern is that I'd only be able to check on the plants once or twice a week and I want to make it as easy as possible on him so my plants will survive. Hopefully if they do better than the tomatoes he has already planted in his backyard garden I can convince him to switch to container gardening and abandon his conventional backyard garden.