Yes, they are perfect for porch pots. As they are annuals in our climactic zone, I imagine they wouldn't need to be all that much larger than the pots they came in. The question is really more one of water retention capability and resistance to wind than of getting potbound too quickly.

I have had a mandevilla in an 18 inch clay pot on our back porch for two years (bringing it in for winter), and it is looking fine. Enjoy!