I grew six Minn. Midget inside/up one 5 ft tomato cage last year and they did well and saved me a lot of space.

spiced_ham Great suggestion; I never thought of growing them up a trellis or a cage. I bet if done right in rich soil they could be planted 2-3ft apart if grown in cages or up a trellis.

Some of them, like Minn. Midg. fall off the vine when ripe so its a good idea to have a soft pad of mulch (grass clippings) for them to fall on.