I think it is difficult to keep the roots cool enough in containers. Try keeping the container well shaded, and the stems should reach up to the light.

You can get trellis designed for pots that some people use successfully. "You tried and failed" sounds so sad. Remember, "To have loved and lost is better than never to have loved at all"

Any of the decorative wire trellises will do. I have a picture posted of a farie with a wire trellis of moderate width and height behind it. Put the pot in front of the trellis and keep the pot shaded and make sure that the area above it is in full sun;the clematis will do the rest as you will see in another photo that I will post tomorrow. If you are seeking to insert the trellis into the pot you can probably find a wire trellis that will fit but not of adequate height once the plant takes off but no problem, buy two trellises of the same type and place one on top of the other by joining them together with plastic electricians tie downs. I have used this method for my potted mandavilla vines as they continue to climb.