My husband badgered me into starting some container-friendly seeds in mid-January.

Unfortunately, at the time I didn't realize Black Cherry tomato plants got as huge as a standard indeterminate, and now we have 5 very happy healthy seedlings growing like weeds and not a clue where we're going to put them.

Planting outside is not an option, my garden is (over)full and by the time tomato planting is too distant still.
I've seen a few posts here and there hinting at successfully growing indeterminates in containers - what size works for you? I'm guessing 5 gallon is too small for most situations, but 15 gal? 20?
Thanks!