Michi -

you better ask a judge from your club. I actually saw people showing their minis in solo cups, but not on the National. There are 2 1/4 (?) size pots very close to 3oz solo cup - so you can just slip your plant into one of these without disturbing the roots. Be sure that you get the set of 2 of appropriate size pots for each plant because on the show - you put a small piece of plastic or foil in the bottom of the empty pot - and slip it on the original pot - so your wick is not touching the table cloth. And you better have both pots the same - not one brown - another one green. Second issue - if minis are more or less minis - semis can grow to the limit of 8" or more. Remove the outer leaves if they grow farther than permitted - and you need to keep the pot 1/3 of the leaf span - so the smallish Solo cup can be too small. (I mean we call them Solo cups - but I saw smaller and larger ones)

I wish you a good crop of Blue Ribbons in March

I.

Solo cups are OK at National and other shows I've attended. Most shows now require slip- potting and the solo cups make it easy. Just slip the one with holes cut in the bottom into a new holeless cup.
Jude