The typical rules for an antweight are, it must fit within a 4 inch cube, and weigh 150 grams or less. They can come across as a lot bigger on camera with some trickery, but they are actually tiiiny. I'm not sure if Robot Wars stuck to the 4 inch cube max size, or just the weight limits.

An arena for antweights is certainly something you can shove in the back of even a decent sized car or MPV and take to anywhere there is interest. if its made portable / modular / flatpack, you might be able to shove it in a backpack and take it on a train. Entertain randomers at Manchester Piccadilly waiting for their delayed trains. (probably not that)