I've got a horticulture book and the section on tomatoes says 'leaf curl isn't harmful to the plant as long as disease or pests aren't present'

Leaves curl on tomatoes when the day and night temps are far apart (hot day, cool night).

So as long as you're pest and disease free they'll be fine. Like the others said though, tomatoes do need huge root systems so they'd be better in the ground or at least in bigger pots - if they get rootbound growth will be stunted and you won't get as many tomatoes.

What 'strain' are the tomatoes?

Good luck.

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